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 $97.96   12.533%   $110.2373   $110.24   $110.25   $110.20  
  Purchase #2 $24.66   6.561%   $26.2779   $26.28   $26.30   $26.30  
  Purchase #3 $105.58   12.675%   $118.9623   $118.96   $118.95   $119.00  
  Purchase #4 $129.96   7.149%   $139.2508   $139.25   $139.25   $139.30  
  Purchase #5 $6.45   3.457%   $6.673   $6.67   $6.65   $6.70  
  Purchase #6 $122.43   11.703%   $136.758   $136.76   $136.75   $136.80  
  Purchase #7 $100.34   13.629%   $114.0153   $114.02   $114.00   $114.00  
  7 purchase totals = $587.38       $652.1746   $652.18   $652.15   $652.30