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 $63.44   6.767%   $67.733   $67.73   $67.75   $67.70  
  Purchase #2 $227.78   6.703%   $243.0481   $243.05   $243.05   $243.00  
  Purchase #3 $77.70   13.839%   $88.4529   $88.45   $88.45   $88.50  
  Purchase #4 $203.36   11.465%   $226.6752   $226.68   $226.70   $226.70  
  Purchase #5 $58.71   8.571%   $63.742   $63.74   $63.75   $63.70  
  Purchase #6 $100.67   8.538%   $109.2652   $109.27   $109.25   $109.30  
  Purchase #7 $107.94   5.669%   $114.0591   $114.06   $114.05   $114.10  
  7 purchase totals = $839.60       $912.9755   $912.98   $913.00   $913.00