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 $45.67   5.723%   $48.2837   $48.28   $48.30   $48.30  
  Purchase #2 $194.48   3.854%   $201.9753   $201.98   $202.00   $202.00  
  Purchase #3 $89.72   9.741%   $98.4596   $98.46   $98.45   $98.50  
  Purchase #4 $132.60   8.155%   $143.4135   $143.41   $143.40   $143.40  
  Purchase #5 $233.84   3.646%   $242.3658   $242.37   $242.35   $242.40  
  Purchase #6 $58.58   8.579%   $63.6056   $63.61   $63.60   $63.60  
  Purchase #7 $28.78   7.321%   $30.887   $30.89   $30.90   $30.90  
  7 purchase totals = $783.67       $828.9905   $829.00   $829.00   $829.10