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 $233.84   13.679%   $265.827   $265.83   $265.85   $265.80  
  Purchase #2 $31.32   13.224%   $35.4618   $35.46   $35.45   $35.50  
  Purchase #3 $205.88   5.606%   $217.4216   $217.42   $217.40   $217.40  
  Purchase #4 $124.59   6.546%   $132.7457   $132.75   $132.75   $132.70  
  Purchase #5 $147.50   8.670%   $160.2883   $160.29   $160.30   $160.30  
  Purchase #6 $73.44   4.824%   $76.9827   $76.98   $77.00   $77.00  
  Purchase #7 $108.29   12.828%   $122.1814   $122.18   $122.20   $122.20  
  7 purchase totals = $924.86       $1,010.9085   $1,010.91   $1,010.95   $1,010.90