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 $179.54   13.253%   $203.3344   $203.33   $203.35   $203.30  
  Purchase #2 $78.86   3.179%   $81.367   $81.37   $81.35   $81.40  
  Purchase #3 $31.99   9.400%   $34.9971   $35.00   $35.00   $35.00  
  Purchase #4 $217.54   12.854%   $245.5026   $245.50   $245.50   $245.50  
  Purchase #5 $35.84   3.607%   $37.1327   $37.13   $37.15   $37.10  
  Purchase #6 $244.53   4.759%   $256.1672   $256.17   $256.15   $256.20  
  Purchase #7 $208.78   7.296%   $224.0126   $224.01   $224.00   $224.00  
  7 purchase totals = $997.08       $1,082.5136   $1,082.51   $1,082.50   $1,082.50