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 $82.45   13.562%   $93.6319   $93.63   $93.65   $93.60  
  Purchase #2 $204.60   4.121%   $213.0316   $213.03   $213.05   $213.00  
  Purchase #3 $91.85   11.151%   $102.0922   $102.09   $102.10   $102.10  
  Purchase #4 $213.53   6.221%   $226.8137   $226.81   $226.80   $226.80  
  Purchase #5 $139.41   6.372%   $148.2932   $148.29   $148.30   $148.30  
  Purchase #6 $162.61   4.633%   $170.1437   $170.14   $170.15   $170.10  
  Purchase #7 $65.68   11.809%   $73.4362   $73.44   $73.45   $73.40  
  7 purchase totals = $960.13       $1,027.4425   $1,027.43   $1,027.50   $1,027.30