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 $56.77   5.376%   $59.822   $59.82   $59.80   $59.80  
  Purchase #2 $143.35   12.571%   $161.3705   $161.37   $161.35   $161.40  
  Purchase #3 $61.59   4.806%   $64.55   $64.55   $64.55   $64.60  
  Purchase #4 $49.41   9.696%   $54.2008   $54.20   $54.20   $54.20  
  Purchase #5 $119.81   5.117%   $125.9407   $125.94   $125.95   $125.90  
  Purchase #6 $192.64   11.128%   $214.077   $214.08   $214.10   $214.10  
  Purchase #7 $95.53   7.575%   $102.7664   $102.77   $102.75   $102.80  
  7 purchase totals = $719.10       $782.7274   $782.73   $782.70   $782.80