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 $89.62   6.277%   $95.2454   $95.25   $95.25   $95.20  
  Purchase #2 $29.69   9.137%   $32.4028   $32.40   $32.40   $32.40  
  Purchase #3 $224.89   10.389%   $248.2538   $248.25   $248.25   $248.30  
  Purchase #4 $160.76   5.743%   $169.9924   $169.99   $170.00   $170.00  
  Purchase #5 $187.85   11.398%   $209.2611   $209.26   $209.25   $209.30  
  Purchase #6 $73.60   7.389%   $79.0383   $79.04   $79.05   $79.00  
  Purchase #7 $219.82   3.768%   $228.1028   $228.10   $228.10   $228.10  
  7 purchase totals = $986.23       $1,062.2966   $1,062.29   $1,062.30   $1,062.30