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 $48.67   11.620%   $54.3255   $54.33   $54.35   $54.30  
  Purchase #2 $229.75   6.368%   $244.3805   $244.38   $244.40   $244.40  
  Purchase #3 $123.99   8.175%   $134.1262   $134.13   $134.15   $134.10  
  Purchase #4 $207.29   3.350%   $214.2342   $214.23   $214.25   $214.20  
  Purchase #5 $138.77   13.513%   $157.522   $157.52   $157.50   $157.50  
  Purchase #6 $203.74   11.741%   $227.6611   $227.66   $227.65   $227.70  
  Purchase #7 $199.37   3.651%   $206.649   $206.65   $206.65   $206.60  
  7 purchase totals = $1,151.58       $1,238.8985   $1,238.90   $1,238.95   $1,238.80