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 $216.86   11.183%   $241.1115   $241.11   $241.10   $241.10  
  Purchase #2 $193.32   5.447%   $203.8501   $203.85   $203.85   $203.90  
  Purchase #3 $76.50   9.573%   $83.8233   $83.82   $83.80   $83.80  
  Purchase #4 $131.77   9.323%   $144.0549   $144.05   $144.05   $144.10  
  Purchase #5 $18.65   9.277%   $20.3802   $20.38   $20.40   $20.40  
  Purchase #6 $34.92   10.714%   $38.6613   $38.66   $38.65   $38.70  
  Purchase #7 $59.89   10.641%   $66.2629   $66.26   $66.25   $66.30  
  7 purchase totals = $731.91       $798.1442   $798.13   $798.10   $798.30