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 $58.69   6.163%   $62.3071   $62.31   $62.30   $62.30  
  Purchase #2 $158.31   3.788%   $164.3068   $164.31   $164.30   $164.30  
  Purchase #3 $246.85   11.147%   $274.3664   $274.37   $274.35   $274.40  
  Purchase #4 $163.47   5.441%   $172.3644   $172.36   $172.35   $172.40  
  Purchase #5 $90.49   5.468%   $95.438   $95.44   $95.45   $95.40  
  Purchase #6 $133.77   11.606%   $149.2953   $149.30   $149.30   $149.30  
  Purchase #7 $100.57   5.568%   $106.1697   $106.17   $106.15   $106.20  
  7 purchase totals = $952.15       $1,024.2477   $1,024.26   $1,024.20   $1,024.30