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 $239.73   9.402%   $262.2694   $262.27   $262.25   $262.30  
  Purchase #2 $36.95   3.172%   $38.1221   $38.12   $38.10   $38.10  
  Purchase #3 $164.67   7.274%   $176.6481   $176.65   $176.65   $176.60  
  Purchase #4 $115.50   10.255%   $127.3445   $127.34   $127.35   $127.30  
  Purchase #5 $209.55   6.844%   $223.8916   $223.89   $223.90   $223.90  
  Purchase #6 $59.53   4.190%   $62.0243   $62.02   $62.00   $62.00  
  Purchase #7 $51.42   13.190%   $58.2023   $58.20   $58.20   $58.20  
  7 purchase totals = $877.35       $948.5023   $948.49   $948.45   $948.40