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 $118.87   4.365%   $124.0587   $124.06   $124.05   $124.10  
  Purchase #2 $141.93   13.362%   $160.8947   $160.89   $160.90   $160.90  
  Purchase #3 $153.98   12.111%   $172.6285   $172.63   $172.65   $172.60  
  Purchase #4 $228.94   8.515%   $248.4342   $248.43   $248.45   $248.40  
  Purchase #5 $226.42   8.494%   $245.6521   $245.65   $245.65   $245.70  
  Purchase #6 $219.33   10.525%   $242.4145   $242.41   $242.40   $242.40  
  Purchase #7 $65.45   4.814%   $68.6008   $68.60   $68.60   $68.60  
  7 purchase totals = $1,154.92       $1,262.6835   $1,262.67   $1,262.70   $1,262.70