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 $68.38   9.739%   $75.0395   $75.04   $75.05   $75.00  
  Purchase #2 $238.91   11.561%   $266.5304   $266.53   $266.55   $266.50  
  Purchase #3 $40.47   9.587%   $44.3499   $44.35   $44.35   $44.30  
  Purchase #4 $166.61   6.868%   $178.0528   $178.05   $178.05   $178.10  
  Purchase #5 $53.44   12.412%   $60.073   $60.07   $60.05   $60.10  
  Purchase #6 $166.56   6.546%   $177.463   $177.46   $177.45   $177.50  
  Purchase #7 $31.94   7.201%   $34.24   $34.24   $34.25   $34.20  
  7 purchase totals = $766.31       $835.7486   $835.74   $835.75   $835.70