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 $61.34   12.453%   $68.9787   $68.98   $69.00   $69.00  
  Purchase #2 $92.38   6.528%   $98.4106   $98.41   $98.40   $98.40  
  Purchase #3 $106.73   11.819%   $119.3444   $119.34   $119.35   $119.30  
  Purchase #4 $120.61   10.581%   $133.3717   $133.37   $133.35   $133.40  
  Purchase #5 $163.81   10.468%   $180.9576   $180.96   $180.95   $181.00  
  Purchase #6 $153.82   9.742%   $168.8051   $168.81   $168.80   $168.80  
  Purchase #7 $198.77   13.823%   $226.246   $226.25   $226.25   $226.20  
  7 purchase totals = $897.46       $996.1141   $996.12   $996.10   $996.10