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 $218.89   13.852%   $249.2106   $249.21   $249.20   $249.20  
  Purchase #2 $207.85   5.492%   $219.2651   $219.27   $219.25   $219.30  
  Purchase #3 $16.94   12.132%   $18.9952   $19.00   $19.00   $19.00  
  Purchase #4 $72.43   11.157%   $80.511   $80.51   $80.50   $80.50  
  Purchase #5 $55.63   10.839%   $61.6597   $61.66   $61.65   $61.70  
  Purchase #6 $100.74   5.245%   $106.0238   $106.02   $106.00   $106.00  
  Purchase #7 $35.54   10.856%   $39.3982   $39.40   $39.40   $39.40  
  7 purchase totals = $708.02       $775.0636   $775.07   $775.00   $775.10