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 $168.55   11.511%   $187.9518   $187.95   $187.95   $188.00  
  Purchase #2 $31.53   10.688%   $34.8999   $34.90   $34.90   $34.90  
  Purchase #3 $240.68   5.325%   $253.4962   $253.50   $253.50   $253.50  
  Purchase #4 $56.78   6.820%   $60.6524   $60.65   $60.65   $60.70  
  Purchase #5 $212.85   10.868%   $235.9825   $235.98   $236.00   $236.00  
  Purchase #6 $76.65   13.193%   $86.7624   $86.76   $86.75   $86.80  
  Purchase #7 $21.25   5.379%   $22.393   $22.39   $22.40   $22.40  
  7 purchase totals = $808.29       $882.1382   $882.13   $882.15   $882.30