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 $9.47   5.146%   $9.9573   $9.96   $9.95   $10.00  
  Purchase #2 $123.94   7.498%   $133.233   $133.23   $133.25   $133.20  
  Purchase #3 $34.37   12.841%   $38.7835   $38.78   $38.80   $38.80  
  Purchase #4 $72.78   5.385%   $76.6992   $76.70   $76.70   $76.70  
  Purchase #5 $84.63   13.829%   $96.3335   $96.33   $96.35   $96.30  
  Purchase #6 $166.43   4.384%   $173.7263   $173.73   $173.75   $173.70  
  Purchase #7 $90.84   12.716%   $102.3912   $102.39   $102.40   $102.40  
  7 purchase totals = $582.46       $631.1240   $631.12   $631.20   $631.10