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 $209.30   8.391%   $226.8624   $226.86   $226.85   $226.90  
  Purchase #2 $46.38   5.762%   $49.0524   $49.05   $49.05   $49.10  
  Purchase #3 $28.66   8.657%   $31.1411   $31.14   $31.15   $31.10  
  Purchase #4 $185.70   5.123%   $195.2134   $195.21   $195.20   $195.20  
  Purchase #5 $94.39   4.498%   $98.6357   $98.64   $98.65   $98.60  
  Purchase #6 $247.48   8.818%   $269.3028   $269.30   $269.30   $269.30  
  Purchase #7 $69.81   6.336%   $74.2332   $74.23   $74.25   $74.20  
  7 purchase totals = $881.72       $944.4410   $944.43   $944.45   $944.40