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 $57.83   8.268%   $62.6114   $62.61   $62.60   $62.60  
  Purchase #2 $245.73   6.613%   $261.9801   $261.98   $262.00   $262.00  
  Purchase #3 $93.44   13.506%   $106.06   $106.06   $106.05   $106.10  
  Purchase #4 $233.29   3.129%   $240.5896   $240.59   $240.60   $240.60  
  Purchase #5 $51.73   3.566%   $53.5747   $53.57   $53.55   $53.60  
  Purchase #6 $215.47   8.488%   $233.7591   $233.76   $233.75   $233.80  
  Purchase #7 $31.56   9.282%   $34.4894   $34.49   $34.50   $34.50  
  7 purchase totals = $929.05       $993.0643   $993.06   $993.05   $993.20