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 $44.66   4.367%   $46.6103   $46.61   $46.60   $46.60  
  Purchase #2 $205.61   8.266%   $222.6057   $222.61   $222.60   $222.60  
  Purchase #3 $157.82   13.546%   $179.1983   $179.20   $179.20   $179.20  
  Purchase #4 $236.53   4.302%   $246.7055   $246.71   $246.70   $246.70  
  Purchase #5 $97.87   12.785%   $110.3827   $110.38   $110.40   $110.40  
  Purchase #6 $36.72   7.565%   $39.4979   $39.50   $39.50   $39.50  
  Purchase #7 $115.89   5.280%   $122.009   $122.01   $122.00   $122.00  
  7 purchase totals = $895.10       $967.0094   $967.02   $967.00   $967.00