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 $68.31   3.692%   $70.832   $70.83   $70.85   $70.80  
  Purchase #2 $207.88   10.372%   $229.4413   $229.44   $229.45   $229.40  
  Purchase #3 $161.51   11.630%   $180.2936   $180.29   $180.30   $180.30  
  Purchase #4 $216.91   4.778%   $227.274   $227.27   $227.25   $227.30  
  Purchase #5 $178.70   11.826%   $199.8331   $199.83   $199.85   $199.80  
  Purchase #6 $171.34   3.313%   $177.0165   $177.02   $177.00   $177.00  
  Purchase #7 $237.33   11.401%   $264.388   $264.39   $264.40   $264.40  
  7 purchase totals = $1,241.98       $1,349.0785   $1,349.07   $1,349.10   $1,349.00