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 $244.29   9.417%   $267.2948   $267.29   $267.30   $267.30  
  Purchase #2 $19.92   6.806%   $21.2758   $21.28   $21.30   $21.30  
  Purchase #3 $49.75   7.779%   $53.6201   $53.62   $53.60   $53.60  
  Purchase #4 $182.88   10.460%   $202.0092   $202.01   $202.00   $202.00  
  Purchase #5 $141.48   5.863%   $149.775   $149.78   $149.80   $149.80  
  Purchase #6 $43.77   5.417%   $46.141   $46.14   $46.15   $46.10  
  Purchase #7 $172.55   6.124%   $183.117   $183.12   $183.10   $183.10  
  7 purchase totals = $854.64       $923.2329   $923.24   $923.25   $923.20