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 $59.96   9.245%   $65.5033   $65.50   $65.50   $65.50  
  Purchase #2 $61.89   11.570%   $69.0507   $69.05   $69.05   $69.10  
  Purchase #3 $58.89   9.873%   $64.7042   $64.70   $64.70   $64.70  
  Purchase #4 $224.57   5.261%   $236.3846   $236.38   $236.40   $236.40  
  Purchase #5 $106.40   11.600%   $118.7424   $118.74   $118.75   $118.70  
  Purchase #6 $158.95   9.201%   $173.575   $173.58   $173.60   $173.60  
  Purchase #7 $237.89   11.267%   $264.6931   $264.69   $264.70   $264.70  
  7 purchase totals = $908.55       $992.6533   $992.64   $992.70   $992.70