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 $235.42   10.684%   $260.5723   $260.57   $260.55   $260.60  
  Purchase #2 $116.98   10.130%   $128.8301   $128.83   $128.85   $128.80  
  Purchase #3 $226.51   4.867%   $237.5342   $237.53   $237.55   $237.50  
  Purchase #4 $200.37   12.659%   $225.7348   $225.73   $225.75   $225.70  
  Purchase #5 $209.58   3.381%   $216.6659   $216.67   $216.65   $216.70  
  Purchase #6 $49.96   10.311%   $55.1114   $55.11   $55.10   $55.10  
  Purchase #7 $74.64   13.174%   $84.4731   $84.47   $84.45   $84.50  
  7 purchase totals = $1,113.46       $1,208.9218   $1,208.91   $1,208.90   $1,208.90