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 $104.65   10.808%   $115.9606   $115.96   $115.95   $116.00  
  Purchase #2 $206.85   5.352%   $217.9206   $217.92   $217.90   $217.90  
  Purchase #3 $54.66   11.673%   $61.0405   $61.04   $61.05   $61.00  
  Purchase #4 $62.77   3.324%   $64.8565   $64.86   $64.85   $64.90  
  Purchase #5 $103.78   11.460%   $115.6732   $115.67   $115.65   $115.70  
  Purchase #6 $64.59   13.716%   $73.4492   $73.45   $73.45   $73.40  
  Purchase #7 $145.75   11.538%   $162.5666   $162.57   $162.55   $162.60  
  7 purchase totals = $743.05       $811.4672   $811.47   $811.40   $811.50