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 $27.41   6.701%   $29.2467   $29.25   $29.25   $29.20  
  Purchase #2 $169.75   12.193%   $190.4476   $190.45   $190.45   $190.40  
  Purchase #3 $113.57   3.273%   $117.2871   $117.29   $117.30   $117.30  
  Purchase #4 $209.49   9.746%   $229.9069   $229.91   $229.90   $229.90  
  Purchase #5 $162.78   13.192%   $184.2539   $184.25   $184.25   $184.30  
  Purchase #6 $29.79   11.840%   $33.3171   $33.32   $33.30   $33.30  
  Purchase #7 $219.54   8.211%   $237.5664   $237.57   $237.55   $237.60  
  7 purchase totals = $932.33       $1,022.0257   $1,022.04   $1,022.00   $1,022.00