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 $212.49   4.816%   $222.7235   $222.72   $222.70   $222.70  
  Purchase #2 $241.57   13.553%   $274.31   $274.31   $274.30   $274.30  
  Purchase #3 $69.78   5.793%   $73.8224   $73.82   $73.80   $73.80  
  Purchase #4 $34.66   12.767%   $39.085   $39.09   $39.10   $39.10  
  Purchase #5 $229.44   12.147%   $257.3101   $257.31   $257.30   $257.30  
  Purchase #6 $92.56   10.130%   $101.9363   $101.94   $101.95   $101.90  
  Purchase #7 $79.66   10.849%   $88.3023   $88.30   $88.30   $88.30  
  7 purchase totals = $960.16       $1,057.4896   $1,057.49   $1,057.45   $1,057.40