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 $61.35   4.232%   $63.9463   $63.95   $63.95   $63.90  
  Purchase #2 $81.27   8.675%   $88.3202   $88.32   $88.30   $88.30  
  Purchase #3 $108.54   4.432%   $113.3505   $113.35   $113.35   $113.40  
  Purchase #4 $22.63   3.673%   $23.4612   $23.46   $23.45   $23.50  
  Purchase #5 $10.94   3.874%   $11.3638   $11.36   $11.35   $11.40  
  Purchase #6 $34.25   6.867%   $36.6019   $36.60   $36.60   $36.60  
  Purchase #7 $222.69   6.865%   $237.9777   $237.98   $238.00   $238.00  
  7 purchase totals = $541.67       $575.0216   $575.02   $575.00   $575.10