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 $213.82   8.482%   $231.9562   $231.96   $231.95   $232.00  
  Purchase #2 $199.34   13.871%   $226.9905   $226.99   $227.00   $227.00  
  Purchase #3 $151.39   12.113%   $169.7279   $169.73   $169.75   $169.70  
  Purchase #4 $43.93   5.517%   $46.3536   $46.35   $46.35   $46.40  
  Purchase #5 $8.49   10.327%   $9.3668   $9.37   $9.35   $9.40  
  Purchase #6 $55.52   13.874%   $63.2228   $63.22   $63.20   $63.20  
  Purchase #7 $208.58   8.362%   $226.0215   $226.02   $226.00   $226.00  
  7 purchase totals = $881.07       $973.6393   $973.64   $973.60   $973.70