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 $248.89   7.683%   $268.0122   $268.01   $268.00   $268.00  
  Purchase #2 $148.51   3.453%   $153.6381   $153.64   $153.65   $153.60  
  Purchase #3 $205.35   6.562%   $218.8251   $218.83   $218.85   $218.80  
  Purchase #4 $129.61   3.754%   $134.4756   $134.48   $134.50   $134.50  
  Purchase #5 $229.85   7.322%   $246.6796   $246.68   $246.70   $246.70  
  Purchase #6 $45.96   5.243%   $48.3697   $48.37   $48.35   $48.40  
  Purchase #7 $156.36   10.593%   $172.9232   $172.92   $172.90   $172.90  
  7 purchase totals = $1,164.53       $1,242.9235   $1,242.93   $1,242.95   $1,242.90