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 $83.99   11.351%   $93.5237   $93.52   $93.50   $93.50  
  Purchase #2 $184.39   4.643%   $192.9512   $192.95   $192.95   $193.00  
  Purchase #3 $61.63   5.461%   $64.9956   $65.00   $65.00   $65.00  
  Purchase #4 $61.35   11.497%   $68.4034   $68.40   $68.40   $68.40  
  Purchase #5 $154.88   9.212%   $169.1475   $169.15   $169.15   $169.10  
  Purchase #6 $225.66   10.771%   $249.9658   $249.97   $249.95   $250.00  
  Purchase #7 $77.59   12.661%   $87.4137   $87.41   $87.40   $87.40  
  7 purchase totals = $849.49       $926.4009   $926.40   $926.35   $926.40