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 $67.86   12.874%   $76.5963   $76.60   $76.60   $76.60  
  Purchase #2 $120.31   13.117%   $136.0911   $136.09   $136.10   $136.10  
  Purchase #3 $23.79   13.401%   $26.9781   $26.98   $27.00   $27.00  
  Purchase #4 $64.58   11.334%   $71.8995   $71.90   $71.90   $71.90  
  Purchase #5 $187.45   12.454%   $210.795   $210.80   $210.80   $210.80  
  Purchase #6 $189.48   5.670%   $200.2235   $200.22   $200.20   $200.20  
  Purchase #7 $148.87   4.308%   $155.2833   $155.28   $155.30   $155.30  
  7 purchase totals = $802.34       $877.8668   $877.87   $877.90   $877.90