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 $41.41   6.561%   $44.1269   $44.13   $44.15   $44.10  
  Purchase #2 $154.52   13.874%   $175.9581   $175.96   $175.95   $176.00  
  Purchase #3 $209.43   6.226%   $222.4691   $222.47   $222.45   $222.50  
  Purchase #4 $105.54   6.138%   $112.018   $112.02   $112.00   $112.00  
  Purchase #5 $68.92   8.334%   $74.6638   $74.66   $74.65   $74.70  
  Purchase #6 $201.42   13.295%   $228.1988   $228.20   $228.20   $228.20  
  Purchase #7 $136.77   6.713%   $145.9514   $145.95   $145.95   $146.00  
  7 purchase totals = $918.01       $1,003.3861   $1,003.39   $1,003.35   $1,003.50