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 $194.44   4.779%   $203.7323   $203.73   $203.75   $203.70  
  Purchase #2 $171.28   8.421%   $185.7035   $185.70   $185.70   $185.70  
  Purchase #3 $158.75   6.673%   $169.3434   $169.34   $169.35   $169.30  
  Purchase #4 $55.83   3.619%   $57.8505   $57.85   $57.85   $57.90  
  Purchase #5 $221.30   7.220%   $237.2779   $237.28   $237.30   $237.30  
  Purchase #6 $200.29   11.332%   $222.9869   $222.99   $223.00   $223.00  
  Purchase #7 $27.35   4.317%   $28.5307   $28.53   $28.55   $28.50  
  7 purchase totals = $1,029.24       $1,105.4252   $1,105.42   $1,105.50   $1,105.40