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 $128.95   10.514%   $142.5078   $142.51   $142.50   $142.50  
  Purchase #2 $244.57   11.589%   $272.9132   $272.91   $272.90   $272.90  
  Purchase #3 $212.78   13.495%   $241.4947   $241.49   $241.50   $241.50  
  Purchase #4 $117.71   13.831%   $133.9905   $133.99   $134.00   $134.00  
  Purchase #5 $80.45   6.284%   $85.5055   $85.51   $85.50   $85.50  
  Purchase #6 $83.93   8.676%   $91.2118   $91.21   $91.20   $91.20  
  Purchase #7 $52.78   6.418%   $56.1674   $56.17   $56.15   $56.20  
  7 purchase totals = $921.17       $1,023.7909   $1,023.79   $1,023.75   $1,023.80