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 $245.48   6.404%   $261.2005   $261.20   $261.20   $261.20  
  Purchase #2 $36.94   10.245%   $40.7245   $40.72   $40.70   $40.70  
  Purchase #3 $232.29   11.249%   $258.4203   $258.42   $258.40   $258.40  
  Purchase #4 $147.39   12.735%   $166.1601   $166.16   $166.15   $166.20  
  Purchase #5 $224.89   7.137%   $240.9404   $240.94   $240.95   $240.90  
  Purchase #6 $200.66   12.146%   $225.0322   $225.03   $225.05   $225.00  
  Purchase #7 $62.77   11.706%   $70.1179   $70.12   $70.10   $70.10  
  7 purchase totals = $1,150.42       $1,262.5959   $1,262.59   $1,262.55   $1,262.50