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 $59.30   11.717%   $66.2482   $66.25   $66.25   $66.20  
  Purchase #2 $188.37   7.409%   $202.3263   $202.33   $202.35   $202.30  
  Purchase #3 $241.86   13.781%   $275.1907   $275.19   $275.20   $275.20  
  Purchase #4 $159.52   13.736%   $181.4317   $181.43   $181.45   $181.40  
  Purchase #5 $78.79   3.328%   $81.4121   $81.41   $81.40   $81.40  
  Purchase #6 $226.60   3.412%   $234.3316   $234.33   $234.35   $234.30  
  Purchase #7 $97.79   6.697%   $104.339   $104.34   $104.35   $104.30  
  7 purchase totals = $1,052.23       $1,145.2796   $1,145.28   $1,145.35   $1,145.10