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 $84.95   9.636%   $93.1358   $93.14   $93.15   $93.10  
  Purchase #2 $165.83   8.164%   $179.3684   $179.37   $179.35   $179.40  
  Purchase #3 $210.45   8.185%   $227.6753   $227.68   $227.70   $227.70  
  Purchase #4 $22.66   8.631%   $24.6158   $24.62   $24.60   $24.60  
  Purchase #5 $217.62   10.474%   $240.4135   $240.41   $240.40   $240.40  
  Purchase #6 $216.55   9.348%   $236.7931   $236.79   $236.80   $236.80  
  Purchase #7 $104.58   7.438%   $112.3587   $112.36   $112.35   $112.40  
  7 purchase totals = $1,022.64       $1,114.3606   $1,114.37   $1,114.35   $1,114.40