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 $144.63   6.294%   $153.733   $153.73   $153.75   $153.70  
  Purchase #2 $61.71   4.823%   $64.6863   $64.69   $64.70   $64.70  
  Purchase #3 $177.36   9.305%   $193.8633   $193.86   $193.85   $193.90  
  Purchase #4 $123.52   11.729%   $138.0077   $138.01   $138.00   $138.00  
  Purchase #5 $118.44   13.142%   $134.0054   $134.01   $134.00   $134.00  
  Purchase #6 $54.38   3.534%   $56.3018   $56.30   $56.30   $56.30  
  Purchase #7 $19.84   8.871%   $21.6   $21.60   $21.60   $21.60  
  7 purchase totals = $699.88       $762.1975   $762.20   $762.20   $762.20