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 $134.73   5.223%   $141.7669   $141.77   $141.75   $141.80  
  Purchase #2 $220.68   10.732%   $244.3634   $244.36   $244.35   $244.40  
  Purchase #3 $74.51   7.250%   $79.912   $79.91   $79.90   $79.90  
  Purchase #4 $132.41   6.853%   $141.4841   $141.48   $141.50   $141.50  
  Purchase #5 $10.78   10.222%   $11.8819   $11.88   $11.90   $11.90  
  Purchase #6 $46.65   4.487%   $48.7432   $48.74   $48.75   $48.70  
  Purchase #7 $181.66   4.247%   $189.3751   $189.38   $189.40   $189.40  
  7 purchase totals = $801.42       $857.5266   $857.52   $857.55   $857.60