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 $86.37   8.239%   $93.486   $93.49   $93.50   $93.50  
  Purchase #2 $245.88   9.581%   $269.4378   $269.44   $269.45   $269.40  
  Purchase #3 $64.70   6.758%   $69.0724   $69.07   $69.05   $69.10  
  Purchase #4 $206.57   5.167%   $217.2435   $217.24   $217.25   $217.20  
  Purchase #5 $39.91   7.470%   $42.8913   $42.89   $42.90   $42.90  
  Purchase #6 $67.76   11.108%   $75.2868   $75.29   $75.30   $75.30  
  Purchase #7 $68.54   3.870%   $71.1925   $71.19   $71.20   $71.20  
  7 purchase totals = $779.73       $838.6103   $838.61   $838.65   $838.60