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 $204.68   12.685%   $230.6437   $230.64   $230.65   $230.60  
  Purchase #2 $139.61   7.104%   $149.5279   $149.53   $149.55   $149.50  
  Purchase #3 $133.30   5.247%   $140.2943   $140.29   $140.30   $140.30  
  Purchase #4 $54.55   13.693%   $62.0195   $62.02   $62.00   $62.00  
  Purchase #5 $233.79   4.119%   $243.4198   $243.42   $243.40   $243.40  
  Purchase #6 $69.36   10.271%   $76.484   $76.48   $76.50   $76.50  
  Purchase #7 $188.32   13.474%   $213.6942   $213.69   $213.70   $213.70  
  7 purchase totals = $1,023.61       $1,116.0834   $1,116.07   $1,116.10   $1,116.00