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 $207.90   8.243%   $225.0372   $225.04   $225.05   $225.00  
  Purchase #2 $189.92   6.587%   $202.43   $202.43   $202.45   $202.40  
  Purchase #3 $28.73   4.202%   $29.9372   $29.94   $29.95   $29.90  
  Purchase #4 $66.29   11.343%   $73.8093   $73.81   $73.80   $73.80  
  Purchase #5 $97.92   5.233%   $103.0442   $103.04   $103.05   $103.00  
  Purchase #6 $200.41   7.409%   $215.2584   $215.26   $215.25   $215.30  
  Purchase #7 $160.53   7.293%   $172.2375   $172.24   $172.25   $172.20  
  7 purchase totals = $951.70       $1,021.7538   $1,021.76   $1,021.80   $1,021.60