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 $215.84   10.566%   $238.6457   $238.65   $238.65   $238.60  
  Purchase #2 $15.95   8.703%   $17.3381   $17.34   $17.35   $17.30  
  Purchase #3 $71.74   12.479%   $80.6924   $80.69   $80.70   $80.70  
  Purchase #4 $118.73   6.788%   $126.7894   $126.79   $126.80   $126.80  
  Purchase #5 $161.73   10.508%   $178.7246   $178.72   $178.70   $178.70  
  Purchase #6 $126.47   12.113%   $141.7893   $141.79   $141.80   $141.80  
  Purchase #7 $86.61   4.601%   $90.5949   $90.59   $90.60   $90.60  
  7 purchase totals = $797.07       $874.5744   $874.57   $874.60   $874.50