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 $66.25   13.202%   $74.9963   $75.00   $75.00   $75.00  
  Purchase #2 $195.77   12.287%   $219.8243   $219.82   $219.80   $219.80  
  Purchase #3 $193.93   13.759%   $220.6128   $220.61   $220.60   $220.60  
  Purchase #4 $231.98   12.432%   $260.8198   $260.82   $260.80   $260.80  
  Purchase #5 $117.81   7.297%   $126.4066   $126.41   $126.40   $126.40  
  Purchase #6 $65.60   13.389%   $74.3832   $74.38   $74.40   $74.40  
  Purchase #7 $172.44   11.459%   $192.1999   $192.20   $192.20   $192.20  
  7 purchase totals = $1,043.78       $1,169.2429   $1,169.24   $1,169.20   $1,169.20