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 $31.33   11.872%   $35.0495   $35.05   $35.05   $35.00  
  Purchase #2 $194.61   11.513%   $217.0154   $217.02   $217.00   $217.00  
  Purchase #3 $92.28   6.129%   $97.9358   $97.94   $97.95   $97.90  
  Purchase #4 $52.96   10.204%   $58.364   $58.36   $58.35   $58.40  
  Purchase #5 $85.92   11.579%   $95.8687   $95.87   $95.85   $95.90  
  Purchase #6 $114.78   11.552%   $128.0394   $128.04   $128.05   $128.00  
  Purchase #7 $110.65   11.235%   $123.0815   $123.08   $123.10   $123.10  
  7 purchase totals = $682.53       $755.3543   $755.36   $755.35   $755.30