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 $153.83   4.823%   $161.2492   $161.25   $161.25   $161.20  
  Purchase #2 $65.52   3.435%   $67.7706   $67.77   $67.75   $67.80  
  Purchase #3 $14.50   9.225%   $15.8376   $15.84   $15.85   $15.80  
  Purchase #4 $202.47   9.408%   $221.5184   $221.52   $221.50   $221.50  
  Purchase #5 $26.87   9.786%   $29.4995   $29.50   $29.50   $29.50  
  Purchase #6 $179.92   11.640%   $200.8627   $200.86   $200.85   $200.90  
  Purchase #7 $26.44   6.567%   $28.1763   $28.18   $28.20   $28.20  
  7 purchase totals = $669.55       $724.9143   $724.92   $724.90   $724.90