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 $39.36   5.281%   $41.4386   $41.44   $41.45   $41.40  
  Purchase #2 $22.88   4.698%   $23.9549   $23.95   $23.95   $24.00  
  Purchase #3 $93.62   9.158%   $102.1937   $102.19   $102.20   $102.20  
  Purchase #4 $217.39   5.224%   $228.7465   $228.75   $228.75   $228.70  
  Purchase #5 $244.55   8.487%   $265.305   $265.31   $265.30   $265.30  
  Purchase #6 $183.61   12.154%   $205.926   $205.93   $205.95   $205.90  
  Purchase #7 $136.87   13.750%   $155.6896   $155.69   $155.70   $155.70  
  7 purchase totals = $938.28       $1,023.2543   $1,023.26   $1,023.30   $1,023.20