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 $56.83   9.271%   $62.0987   $62.10   $62.10   $62.10  
  Purchase #2 $191.25   6.141%   $202.9947   $202.99   $203.00   $203.00  
  Purchase #3 $167.45   3.209%   $172.8235   $172.82   $172.80   $172.80  
  Purchase #4 $216.66   5.742%   $229.1006   $229.10   $229.10   $229.10  
  Purchase #5 $83.99   4.522%   $87.788   $87.79   $87.80   $87.80  
  Purchase #6 $161.48   7.384%   $173.4037   $173.40   $173.40   $173.40  
  Purchase #7 $229.50   11.452%   $255.7823   $255.78   $255.80   $255.80  
  7 purchase totals = $1,107.16       $1,183.9915   $1,183.98   $1,184.00   $1,184.00