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 $52.46   13.515%   $59.55   $59.55   $59.55   $59.60  
  Purchase #2 $233.84   10.502%   $258.3979   $258.40   $258.40   $258.40  
  Purchase #3 $238.51   11.835%   $266.7377   $266.74   $266.75   $266.70  
  Purchase #4 $193.84   8.464%   $210.2466   $210.25   $210.25   $210.20  
  Purchase #5 $160.85   11.269%   $178.9762   $178.98   $179.00   $179.00  
  Purchase #6 $199.98   12.290%   $224.5575   $224.56   $224.55   $224.60  
  Purchase #7 $89.95   7.214%   $96.439   $96.44   $96.45   $96.40  
  7 purchase totals = $1,169.43       $1,294.9049   $1,294.92   $1,294.95   $1,294.90