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 $51.68   12.732%   $58.2599   $58.26   $58.25   $58.30  
  Purchase #2 $214.97   5.697%   $227.2168   $227.22   $227.20   $227.20  
  Purchase #3 $97.90   9.288%   $106.993   $106.99   $107.00   $107.00  
  Purchase #4 $184.94   12.231%   $207.56   $207.56   $207.55   $207.60  
  Purchase #5 $136.59   8.760%   $148.5553   $148.56   $148.55   $148.60  
  Purchase #6 $30.61   3.684%   $31.7377   $31.74   $31.75   $31.70  
  Purchase #7 $222.56   7.728%   $239.7594   $239.76   $239.75   $239.80  
  7 purchase totals = $939.25       $1,020.0821   $1,020.09   $1,020.05   $1,020.20