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 $235.50   12.581%   $265.1283   $265.13   $265.15   $265.10  
  Purchase #2 $131.66   9.256%   $143.8464   $143.85   $143.85   $143.80  
  Purchase #3 $220.40   7.143%   $236.1432   $236.14   $236.15   $236.10  
  Purchase #4 $69.33   11.443%   $77.2634   $77.26   $77.25   $77.30  
  Purchase #5 $59.64   4.525%   $62.3387   $62.34   $62.35   $62.30  
  Purchase #6 $66.62   11.377%   $74.1994   $74.20   $74.20   $74.20  
  Purchase #7 $225.45   7.782%   $242.9945   $242.99   $243.00   $243.00  
  7 purchase totals = $1,008.60       $1,101.9139   $1,101.91   $1,101.95   $1,101.80