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 $238.90   3.495%   $247.2496   $247.25   $247.25   $247.20  
  Purchase #2 $98.71   9.272%   $107.8624   $107.86   $107.85   $107.90  
  Purchase #3 $161.25   9.695%   $176.8832   $176.88   $176.90   $176.90  
  Purchase #4 $204.27   6.181%   $216.8959   $216.90   $216.90   $216.90  
  Purchase #5 $163.87   9.132%   $178.8346   $178.83   $178.85   $178.80  
  Purchase #6 $235.88   12.300%   $264.8932   $264.89   $264.90   $264.90  
  Purchase #7 $230.46   3.568%   $238.6828   $238.68   $238.70   $238.70  
  7 purchase totals = $1,333.34       $1,431.3017   $1,431.29   $1,431.35   $1,431.30