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 $60.58   11.560%   $67.583   $67.58   $67.60   $67.60  
  Purchase #2 $184.53   10.749%   $204.3651   $204.37   $204.35   $204.40  
  Purchase #3 $102.33   7.556%   $110.0621   $110.06   $110.05   $110.10  
  Purchase #4 $31.77   11.479%   $35.4169   $35.42   $35.40   $35.40  
  Purchase #5 $101.87   4.249%   $106.1985   $106.20   $106.20   $106.20  
  Purchase #6 $189.91   12.712%   $214.0514   $214.05   $214.05   $214.10  
  Purchase #7 $88.30   8.126%   $95.4753   $95.48   $95.50   $95.50  
  7 purchase totals = $759.29       $833.1523   $833.16   $833.15   $833.30