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 $226.85   13.780%   $258.1099   $258.11   $258.10   $258.10  
  Purchase #2 $194.92   12.689%   $219.6534   $219.65   $219.65   $219.70  
  Purchase #3 $57.62   9.754%   $63.2403   $63.24   $63.25   $63.20  
  Purchase #4 $16.88   8.462%   $18.3084   $18.31   $18.30   $18.30  
  Purchase #5 $225.29   9.829%   $247.4338   $247.43   $247.45   $247.40  
  Purchase #6 $92.64   4.743%   $97.0339   $97.03   $97.05   $97.00  
  Purchase #7 $159.96   4.576%   $167.2798   $167.28   $167.30   $167.30  
  7 purchase totals = $974.16       $1,071.0595   $1,071.05   $1,071.10   $1,071.00