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 $186.39   11.304%   $207.4595   $207.46   $207.45   $207.50  
  Purchase #2 $146.87   11.281%   $163.4384   $163.44   $163.45   $163.40  
  Purchase #3 $143.59   10.273%   $158.341   $158.34   $158.35   $158.30  
  Purchase #4 $141.53   13.484%   $160.6139   $160.61   $160.60   $160.60  
  Purchase #5 $99.25   4.808%   $104.0219   $104.02   $104.00   $104.00  
  Purchase #6 $176.26   5.224%   $185.4678   $185.47   $185.45   $185.50  
  Purchase #7 $60.96   8.663%   $66.241   $66.24   $66.25   $66.20  
  7 purchase totals = $954.85       $1,045.5835   $1,045.58   $1,045.55   $1,045.50