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 $13.58   8.698%   $14.7612   $14.76   $14.75   $14.80  
  Purchase #2 $208.61   11.339%   $232.2643   $232.26   $232.25   $232.30  
  Purchase #3 $81.73   8.864%   $88.9745   $88.97   $88.95   $89.00  
  Purchase #4 $78.81   12.227%   $88.4461   $88.45   $88.45   $88.40  
  Purchase #5 $95.36   10.605%   $105.4729   $105.47   $105.45   $105.50  
  Purchase #6 $220.60   10.461%   $243.677   $243.68   $243.70   $243.70  
  Purchase #7 $160.76   6.655%   $171.4586   $171.46   $171.45   $171.50  
  7 purchase totals = $859.45       $945.0546   $945.05   $945.00   $945.20