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 $237.47   7.702%   $255.7599   $255.76   $255.75   $255.80  
  Purchase #2 $209.46   13.786%   $238.3362   $238.34   $238.35   $238.30  
  Purchase #3 $60.32   7.275%   $64.7083   $64.71   $64.70   $64.70  
  Purchase #4 $116.35   5.401%   $122.6341   $122.63   $122.65   $122.60  
  Purchase #5 $224.50   4.674%   $234.9931   $234.99   $235.00   $235.00  
  Purchase #6 $54.34   3.607%   $56.3   $56.30   $56.30   $56.30  
  Purchase #7 $88.96   5.752%   $94.077   $94.08   $94.10   $94.10  
  7 purchase totals = $991.40       $1,066.8086   $1,066.81   $1,066.85   $1,066.80