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 $214.83   11.523%   $239.5849   $239.58   $239.60   $239.60  
  Purchase #2 $141.59   5.214%   $148.9725   $148.97   $148.95   $149.00  
  Purchase #3 $224.43   6.617%   $239.2805   $239.28   $239.30   $239.30  
  Purchase #4 $73.69   8.728%   $80.1217   $80.12   $80.10   $80.10  
  Purchase #5 $114.66   8.829%   $124.7833   $124.78   $124.80   $124.80  
  Purchase #6 $209.53   5.430%   $220.9075   $220.91   $220.90   $220.90  
  Purchase #7 $107.60   9.646%   $117.9791   $117.98   $118.00   $118.00  
  7 purchase totals = $1,086.33       $1,171.6295   $1,171.62   $1,171.65   $1,171.70