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 $53.35   13.447%   $60.524   $60.52   $60.50   $60.50  
  Purchase #2 $23.72   7.171%   $25.421   $25.42   $25.40   $25.40  
  Purchase #3 $93.33   13.856%   $106.2618   $106.26   $106.25   $106.30  
  Purchase #4 $64.60   12.707%   $72.8087   $72.81   $72.80   $72.80  
  Purchase #5 $229.26   9.538%   $251.1268   $251.13   $251.15   $251.10  
  Purchase #6 $119.89   6.697%   $127.919   $127.92   $127.90   $127.90  
  Purchase #7 $70.90   7.499%   $76.2168   $76.22   $76.20   $76.20  
  7 purchase totals = $655.05       $720.2781   $720.28   $720.20   $720.20