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 $141.98   11.700%   $158.5917   $158.59   $158.60   $158.60  
  Purchase #2 $234.55   5.301%   $246.9835   $246.98   $247.00   $247.00  
  Purchase #3 $163.70   11.292%   $182.185   $182.19   $182.20   $182.20  
  Purchase #4 $231.53   5.187%   $243.5395   $243.54   $243.55   $243.50  
  Purchase #5 $209.64   11.797%   $234.3712   $234.37   $234.35   $234.40  
  Purchase #6 $57.55   13.265%   $65.184   $65.18   $65.20   $65.20  
  Purchase #7 $135.33   4.629%   $141.5944   $141.59   $141.60   $141.60  
  7 purchase totals = $1,174.28       $1,272.4493   $1,272.44   $1,272.50   $1,272.50