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 $27.43   4.544%   $28.6764   $28.68   $28.70   $28.70  
  Purchase #2 $163.61   5.201%   $172.1194   $172.12   $172.10   $172.10  
  Purchase #3 $157.70   9.285%   $172.3424   $172.34   $172.35   $172.30  
  Purchase #4 $28.32   3.673%   $29.3602   $29.36   $29.35   $29.40  
  Purchase #5 $187.43   9.338%   $204.9322   $204.93   $204.95   $204.90  
  Purchase #6 $84.35   6.343%   $89.7003   $89.70   $89.70   $89.70  
  Purchase #7 $141.86   8.725%   $154.2373   $154.24   $154.25   $154.20  
  7 purchase totals = $790.70       $851.3682   $851.37   $851.40   $851.30