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 $56.99   8.803%   $62.0068   $62.01   $62.00   $62.00  
  Purchase #2 $171.94   12.230%   $192.9683   $192.97   $192.95   $193.00  
  Purchase #3 $88.40   13.599%   $100.4215   $100.42   $100.40   $100.40  
  Purchase #4 $24.59   5.515%   $25.9461   $25.95   $25.95   $25.90  
  Purchase #5 $191.32   5.163%   $201.1979   $201.20   $201.20   $201.20  
  Purchase #6 $197.31   13.577%   $224.0988   $224.10   $224.10   $224.10  
  Purchase #7 $101.79   3.670%   $105.5257   $105.53   $105.55   $105.50  
  7 purchase totals = $832.34       $912.1651   $912.18   $912.15   $912.10