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 $190.65   6.155%   $202.3845   $202.38   $202.40   $202.40  
  Purchase #2 $122.41   13.325%   $138.7211   $138.72   $138.70   $138.70  
  Purchase #3 $163.56   7.585%   $175.966   $175.97   $175.95   $176.00  
  Purchase #4 $161.43   13.228%   $182.784   $182.78   $182.80   $182.80  
  Purchase #5 $152.91   5.634%   $161.5249   $161.52   $161.50   $161.50  
  Purchase #6 $98.59   5.779%   $104.2875   $104.29   $104.30   $104.30  
  Purchase #7 $234.45   11.185%   $260.6732   $260.67   $260.65   $260.70  
  7 purchase totals = $1,124.00       $1,226.3412   $1,226.33   $1,226.30   $1,226.40