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 $192.60   6.257%   $204.651   $204.65   $204.65   $204.70  
  Purchase #2 $85.39   9.468%   $93.4747   $93.47   $93.45   $93.50  
  Purchase #3 $201.63   3.709%   $209.1085   $209.11   $209.10   $209.10  
  Purchase #4 $185.48   7.488%   $199.3687   $199.37   $199.35   $199.40  
  Purchase #5 $240.34   11.537%   $268.068   $268.07   $268.05   $268.10  
  Purchase #6 $95.91   10.779%   $106.2481   $106.25   $106.25   $106.20  
  Purchase #7 $178.39   3.371%   $184.4035   $184.40   $184.40   $184.40  
  7 purchase totals = $1,179.74       $1,265.3225   $1,265.32   $1,265.25   $1,265.40