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 $146.70   13.657%   $166.7348   $166.73   $166.75   $166.70  
  Purchase #2 $183.95   8.740%   $200.0272   $200.03   $200.05   $200.00  
  Purchase #3 $57.74   11.788%   $64.5464   $64.55   $64.55   $64.50  
  Purchase #4 $233.93   4.435%   $244.3048   $244.30   $244.30   $244.30  
  Purchase #5 $159.72   7.346%   $171.453   $171.45   $171.45   $171.50  
  Purchase #6 $227.51   10.310%   $250.9663   $250.97   $250.95   $251.00  
  Purchase #7 $85.39   12.616%   $96.1628   $96.16   $96.15   $96.20  
  7 purchase totals = $1,094.94       $1,194.1953   $1,194.19   $1,194.20   $1,194.20