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 $176.67   13.211%   $200.0099   $200.01   $200.00   $200.00  
  Purchase #2 $243.74   6.338%   $259.1882   $259.19   $259.20   $259.20  
  Purchase #3 $157.76   12.107%   $176.86   $176.86   $176.85   $176.90  
  Purchase #4 $21.93   8.796%   $23.859   $23.86   $23.85   $23.90  
  Purchase #5 $75.53   3.555%   $78.2151   $78.22   $78.20   $78.20  
  Purchase #6 $43.88   4.717%   $45.9498   $45.95   $45.95   $45.90  
  Purchase #7 $42.75   13.405%   $48.4806   $48.48   $48.50   $48.50  
  7 purchase totals = $762.26       $832.5626   $832.57   $832.55   $832.60