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 $211.86   12.223%   $237.7556   $237.76   $237.75   $237.80  
  Purchase #2 $169.37   13.569%   $192.3518   $192.35   $192.35   $192.40  
  Purchase #3 $193.90   8.227%   $209.8522   $209.85   $209.85   $209.90  
  Purchase #4 $48.78   6.742%   $52.0687   $52.07   $52.05   $52.10  
  Purchase #5 $118.74   13.205%   $134.4196   $134.42   $134.40   $134.40  
  Purchase #6 $95.71   10.570%   $105.8265   $105.83   $105.85   $105.80  
  Purchase #7 $29.65   4.856%   $31.0898   $31.09   $31.10   $31.10  
  7 purchase totals = $868.01       $963.3642   $963.37   $963.35   $963.50