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 $214.39   10.126%   $236.0991   $236.10   $236.10   $236.10  
  Purchase #2 $220.33   3.313%   $227.6295   $227.63   $227.65   $227.60  
  Purchase #3 $99.29   5.303%   $104.5553   $104.56   $104.55   $104.60  
  Purchase #4 $57.99   13.308%   $65.7073   $65.71   $65.70   $65.70  
  Purchase #5 $60.94   5.762%   $64.4514   $64.45   $64.45   $64.50  
  Purchase #6 $238.50   4.434%   $249.0751   $249.08   $249.10   $249.10  
  Purchase #7 $121.88   13.476%   $138.3045   $138.30   $138.30   $138.30  
  7 purchase totals = $1,013.32       $1,085.8222   $1,085.83   $1,085.85   $1,085.90