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 $68.30   7.794%   $73.6233   $73.62   $73.60   $73.60  
  Purchase #2 $240.59   9.308%   $262.9841   $262.98   $263.00   $263.00  
  Purchase #3 $65.77   9.843%   $72.2437   $72.24   $72.25   $72.20  
  Purchase #4 $31.78   12.189%   $35.6537   $35.65   $35.65   $35.70  
  Purchase #5 $130.62   10.149%   $143.8766   $143.88   $143.90   $143.90  
  Purchase #6 $250.98   5.142%   $263.8854   $263.89   $263.90   $263.90  
  Purchase #7 $160.82   13.170%   $182   $182.00   $182.00   $182.00  
  7 purchase totals = $948.86       $1,034.2668   $1,034.26   $1,034.30   $1,034.30