Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.58   5.528%   $123.0245   $123.02   $123.00   $123.00  
  Purchase #2 $165.69   10.387%   $182.9002   $182.90   $182.90   $182.90  
  Purchase #3 $245.29   6.663%   $261.6337   $261.63   $261.65   $261.60  
  Purchase #4 $107.97   10.254%   $119.0412   $119.04   $119.05   $119.00  
  Purchase #5 $205.96   5.783%   $217.8707   $217.87   $217.85   $217.90  
  Purchase #6 $226.94   12.190%   $254.604   $254.60   $254.60   $254.60  
  Purchase #7 $162.95   11.668%   $181.963   $181.96   $181.95   $182.00  
  7 purchase totals = $1,231.38       $1,341.0373   $1,341.02   $1,341.00   $1,341.00