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 $13.73   6.326%   $14.5986   $14.60   $14.60   $14.60  
  Purchase #2 $194.29   11.511%   $216.6547   $216.65   $216.65   $216.70  
  Purchase #3 $237.90   4.431%   $248.4413   $248.44   $248.45   $248.40  
  Purchase #4 $14.74   13.457%   $16.7236   $16.72   $16.70   $16.70  
  Purchase #5 $206.37   12.727%   $232.6347   $232.63   $232.65   $232.60  
  Purchase #6 $138.74   9.450%   $151.8509   $151.85   $151.85   $151.90  
  Purchase #7 $239.57   8.613%   $260.2042   $260.20   $260.20   $260.20  
  7 purchase totals = $1,045.34       $1,141.1080   $1,141.09   $1,141.10   $1,141.10