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 $23.28   11.223%   $25.8927   $25.89   $25.90   $25.90  
  Purchase #2 $124.71   3.383%   $128.9289   $128.93   $128.95   $128.90  
  Purchase #3 $116.58   5.149%   $122.5827   $122.58   $122.60   $122.60  
  Purchase #4 $181.97   9.163%   $198.6439   $198.64   $198.65   $198.60  
  Purchase #5 $120.47   11.329%   $134.118   $134.12   $134.10   $134.10  
  Purchase #6 $97.74   10.461%   $107.9646   $107.96   $107.95   $108.00  
  Purchase #7 $18.74   11.327%   $20.8627   $20.86   $20.85   $20.90  
  7 purchase totals = $683.49       $738.9935   $738.98   $739.00   $739.00