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 $242.98   4.411%   $253.6978   $253.70   $253.70   $253.70  
  Purchase #2 $212.62   4.276%   $221.7116   $221.71   $221.70   $221.70  
  Purchase #3 $223.80   12.597%   $251.9921   $251.99   $252.00   $252.00  
  Purchase #4 $34.43   4.635%   $36.0258   $36.03   $36.05   $36.00  
  Purchase #5 $217.27   8.745%   $236.2703   $236.27   $236.25   $236.30  
  Purchase #6 $45.76   5.488%   $48.2713   $48.27   $48.25   $48.30  
  Purchase #7 $17.25   5.707%   $18.2345   $18.23   $18.25   $18.20  
  7 purchase totals = $994.11       $1,066.2034   $1,066.20   $1,066.20   $1,066.20