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 $72.50   7.628%   $78.0303   $78.03   $78.05   $78.00  
  Purchase #2 $113.63   11.735%   $126.9645   $126.96   $126.95   $127.00  
  Purchase #3 $87.27   11.178%   $97.025   $97.03   $97.05   $97.00  
  Purchase #4 $70.63   4.853%   $74.0577   $74.06   $74.05   $74.10  
  Purchase #5 $182.41   10.196%   $201.0085   $201.01   $201.00   $201.00  
  Purchase #6 $124.46   10.454%   $137.471   $137.47   $137.45   $137.50  
  Purchase #7 $167.46   9.200%   $182.8663   $182.87   $182.85   $182.90  
  7 purchase totals = $818.36       $897.4233   $897.43   $897.40   $897.50