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 $82.76   12.818%   $93.3682   $93.37   $93.35   $93.40  
  Purchase #2 $223.27   5.599%   $235.7709   $235.77   $235.75   $235.80  
  Purchase #3 $31.60   4.572%   $33.0448   $33.04   $33.05   $33.00  
  Purchase #4 $156.99   5.669%   $165.8898   $165.89   $165.90   $165.90  
  Purchase #5 $105.97   7.526%   $113.9453   $113.95   $113.95   $113.90  
  Purchase #6 $147.99   8.757%   $160.9495   $160.95   $160.95   $160.90  
  Purchase #7 $244.44   4.272%   $254.8825   $254.88   $254.90   $254.90  
  7 purchase totals = $993.02       $1,057.8510   $1,057.85   $1,057.85   $1,057.80