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 $83.49   11.111%   $92.7666   $92.77   $92.75   $92.80  
  Purchase #2 $32.49   8.454%   $35.2367   $35.24   $35.25   $35.20  
  Purchase #3 $26.76   9.715%   $29.3597   $29.36   $29.35   $29.40  
  Purchase #4 $201.51   10.614%   $222.8983   $222.90   $222.90   $222.90  
  Purchase #5 $157.57   9.618%   $172.7251   $172.73   $172.75   $172.70  
  Purchase #6 $242.87   4.764%   $254.4403   $254.44   $254.45   $254.40  
  Purchase #7 $195.64   7.633%   $210.5732   $210.57   $210.55   $210.60  
  7 purchase totals = $940.33       $1,017.9999   $1,018.01   $1,018.00   $1,018.00