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 $146.96   7.390%   $157.8203   $157.82   $157.80   $157.80  
  Purchase #2 $192.50   4.236%   $200.6543   $200.65   $200.65   $200.70  
  Purchase #3 $55.87   7.618%   $60.1262   $60.13   $60.15   $60.10  
  Purchase #4 $98.71   3.749%   $102.4106   $102.41   $102.40   $102.40  
  Purchase #5 $9.59   7.786%   $10.3367   $10.34   $10.35   $10.30  
  Purchase #6 $233.71   7.635%   $251.5538   $251.55   $251.55   $251.60  
  Purchase #7 $250.78   4.790%   $262.7924   $262.79   $262.80   $262.80  
  7 purchase totals = $988.12       $1,045.6943   $1,045.69   $1,045.70   $1,045.70