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 $68.73   6.662%   $73.3088   $73.31   $73.30   $73.30  
  Purchase #2 $205.75   10.611%   $227.5821   $227.58   $227.60   $227.60  
  Purchase #3 $16.35   10.453%   $18.0591   $18.06   $18.05   $18.10  
  Purchase #4 $180.52   8.283%   $195.4725   $195.47   $195.45   $195.50  
  Purchase #5 $204.63   10.622%   $226.3658   $226.37   $226.35   $226.40  
  Purchase #6 $151.39   9.606%   $165.9325   $165.93   $165.95   $165.90  
  Purchase #7 $168.30   12.331%   $189.0531   $189.05   $189.05   $189.10  
  7 purchase totals = $995.67       $1,095.7739   $1,095.77   $1,095.75   $1,095.90