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 $73.91   3.104%   $76.2042   $76.20   $76.20   $76.20  
  Purchase #2 $97.44   10.611%   $107.7794   $107.78   $107.80   $107.80  
  Purchase #3 $208.55   10.177%   $229.7741   $229.77   $229.75   $229.80  
  Purchase #4 $224.48   10.466%   $247.9741   $247.97   $247.95   $248.00  
  Purchase #5 $144.70   7.815%   $156.0083   $156.01   $156.00   $156.00  
  Purchase #6 $62.60   10.267%   $69.0271   $69.03   $69.05   $69.00  
  Purchase #7 $46.54   9.837%   $51.1181   $51.12   $51.10   $51.10  
  7 purchase totals = $858.22       $937.8853   $937.88   $937.85   $937.90