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 $46.45   13.149%   $52.5577   $52.56   $52.55   $52.60  
  Purchase #2 $205.76   7.545%   $221.2846   $221.28   $221.30   $221.30  
  Purchase #3 $216.89   8.529%   $235.3885   $235.39   $235.40   $235.40  
  Purchase #4 $32.26   8.563%   $35.0224   $35.02   $35.00   $35.00  
  Purchase #5 $59.99   13.781%   $68.2572   $68.26   $68.25   $68.30  
  Purchase #6 $165.55   7.516%   $177.9927   $177.99   $178.00   $178.00  
  Purchase #7 $38.51   3.399%   $39.819   $39.82   $39.80   $39.80  
  7 purchase totals = $765.41       $830.3221   $830.32   $830.30   $830.40