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 $140.87   9.441%   $154.1695   $154.17   $154.15   $154.20  
  Purchase #2 $233.84   12.348%   $262.7146   $262.71   $262.70   $262.70  
  Purchase #3 $221.32   3.371%   $228.7807   $228.78   $228.80   $228.80  
  Purchase #4 $51.64   13.565%   $58.645   $58.65   $58.65   $58.60  
  Purchase #5 $153.76   3.118%   $158.5542   $158.55   $158.55   $158.60  
  Purchase #6 $14.47   11.374%   $16.1158   $16.12   $16.10   $16.10  
  Purchase #7 $63.34   13.471%   $71.8725   $71.87   $71.85   $71.90  
  7 purchase totals = $879.24       $950.8523   $950.85   $950.80   $950.90