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 $242.32   13.863%   $275.9128   $275.91   $275.90   $275.90  
  Purchase #2 $87.86   11.230%   $97.7267   $97.73   $97.75   $97.70  
  Purchase #3 $143.50   4.638%   $150.1555   $150.16   $150.15   $150.20  
  Purchase #4 $248.91   13.703%   $283.0181   $283.02   $283.00   $283.00  
  Purchase #5 $179.42   5.746%   $189.7295   $189.73   $189.75   $189.70  
  Purchase #6 $56.80   13.216%   $64.3067   $64.31   $64.30   $64.30  
  Purchase #7 $123.25   9.664%   $135.1609   $135.16   $135.15   $135.20  
  7 purchase totals = $1,082.06       $1,196.0102   $1,196.02   $1,196.00   $1,196.00