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 $93.86   3.716%   $97.3478   $97.35   $97.35   $97.30  
  Purchase #2 $31.52   12.291%   $35.3941   $35.39   $35.40   $35.40  
  Purchase #3 $203.73   3.750%   $211.3699   $211.37   $211.35   $211.40  
  Purchase #4 $57.56   4.231%   $59.9954   $60.00   $60.00   $60.00  
  Purchase #5 $176.78   12.712%   $199.2523   $199.25   $199.25   $199.30  
  Purchase #6 $140.30   5.225%   $147.6307   $147.63   $147.65   $147.60  
  Purchase #7 $21.74   12.161%   $24.3838   $24.38   $24.40   $24.40  
  7 purchase totals = $725.49       $775.3740   $775.37   $775.40   $775.40