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 $22.68   11.176%   $25.2147   $25.21   $25.20   $25.20  
  Purchase #2 $93.87   12.123%   $105.2499   $105.25   $105.25   $105.20  
  Purchase #3 $220.29   9.631%   $241.5061   $241.51   $241.50   $241.50  
  Purchase #4 $183.42   5.730%   $193.93   $193.93   $193.95   $193.90  
  Purchase #5 $179.45   11.129%   $199.421   $199.42   $199.40   $199.40  
  Purchase #6 $57.27   3.558%   $59.3077   $59.31   $59.30   $59.30  
  Purchase #7 $139.31   7.196%   $149.3347   $149.33   $149.35   $149.30  
  7 purchase totals = $896.29       $973.9641   $973.96   $973.95   $973.80