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 $194.35   3.805%   $201.745   $201.75   $201.75   $201.70  
  Purchase #2 $85.62   5.451%   $90.2871   $90.29   $90.30   $90.30  
  Purchase #3 $65.63   11.421%   $73.1256   $73.13   $73.15   $73.10  
  Purchase #4 $91.95   3.839%   $95.48   $95.48   $95.50   $95.50  
  Purchase #5 $168.91   13.863%   $192.326   $192.33   $192.35   $192.30  
  Purchase #6 $106.59   8.231%   $115.3634   $115.36   $115.35   $115.40  
  Purchase #7 $11.94   5.700%   $12.6206   $12.62   $12.60   $12.60  
  7 purchase totals = $724.99       $780.9477   $780.96   $781.00   $780.90