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 $240.73   6.160%   $255.559   $255.56   $255.55   $255.60  
  Purchase #2 $72.57   3.318%   $74.9779   $74.98   $75.00   $75.00  
  Purchase #3 $151.31   7.391%   $162.4933   $162.49   $162.50   $162.50  
  Purchase #4 $244.49   13.652%   $277.8678   $277.87   $277.85   $277.90  
  Purchase #5 $92.81   6.286%   $98.644   $98.64   $98.65   $98.60  
  Purchase #6 $182.35   12.358%   $204.8848   $204.88   $204.90   $204.90  
  Purchase #7 $44.72   6.482%   $47.6188   $47.62   $47.60   $47.60  
  7 purchase totals = $1,028.98       $1,122.0456   $1,122.04   $1,122.05   $1,122.10