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 $151.71   11.216%   $168.7258   $168.73   $168.75   $168.70  
  Purchase #2 $193.41   11.600%   $215.8456   $215.85   $215.85   $215.80  
  Purchase #3 $154.65   5.239%   $162.7521   $162.75   $162.75   $162.80  
  Purchase #4 $139.71   9.601%   $153.1236   $153.12   $153.10   $153.10  
  Purchase #5 $146.87   4.764%   $153.8669   $153.87   $153.85   $153.90  
  Purchase #6 $185.70   11.751%   $207.5216   $207.52   $207.50   $207.50  
  Purchase #7 $173.72   10.799%   $192.48   $192.48   $192.50   $192.50  
  7 purchase totals = $1,145.77       $1,254.3156   $1,254.32   $1,254.30   $1,254.30