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 $57.71   10.841%   $63.9663   $63.97   $63.95   $64.00  
  Purchase #2 $232.76   3.372%   $240.6087   $240.61   $240.60   $240.60  
  Purchase #3 $234.60   8.275%   $254.0132   $254.01   $254.00   $254.00  
  Purchase #4 $182.78   12.859%   $206.2837   $206.28   $206.30   $206.30  
  Purchase #5 $127.50   12.740%   $143.7435   $143.74   $143.75   $143.70  
  Purchase #6 $246.95   12.209%   $277.1001   $277.10   $277.10   $277.10  
  Purchase #7 $142.94   6.575%   $152.3383   $152.34   $152.35   $152.30  
  7 purchase totals = $1,225.24       $1,338.0538   $1,338.05   $1,338.05   $1,338.00