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 $57.61   9.867%   $63.2944   $63.29   $63.30   $63.30  
  Purchase #2 $186.99   4.290%   $195.0119   $195.01   $195.00   $195.00  
  Purchase #3 $114.62   8.216%   $124.0372   $124.04   $124.05   $124.00  
  Purchase #4 $77.32   12.714%   $87.1505   $87.15   $87.15   $87.20  
  Purchase #5 $171.25   11.812%   $191.4781   $191.48   $191.50   $191.50  
  Purchase #6 $25.55   5.145%   $26.8645   $26.86   $26.85   $26.90  
  Purchase #7 $216.61   12.736%   $244.1974   $244.20   $244.20   $244.20  
  7 purchase totals = $849.95       $932.0340   $932.03   $932.05   $932.10