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 $73.62   12.169%   $82.5788   $82.58   $82.60   $82.60  
  Purchase #2 $171.44   13.122%   $193.9364   $193.94   $193.95   $193.90  
  Purchase #3 $70.26   3.739%   $72.887   $72.89   $72.90   $72.90  
  Purchase #4 $29.76   9.640%   $32.6289   $32.63   $32.65   $32.60  
  Purchase #5 $171.89   11.498%   $191.6539   $191.65   $191.65   $191.70  
  Purchase #6 $244.54   5.501%   $257.9921   $257.99   $258.00   $258.00  
  Purchase #7 $60.30   4.687%   $63.1263   $63.13   $63.15   $63.10  
  7 purchase totals = $821.81       $894.8034   $894.81   $894.90   $894.80