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 $58.66   10.662%   $64.9143   $64.91   $64.90   $64.90  
  Purchase #2 $168.76   13.166%   $190.9789   $190.98   $191.00   $191.00  
  Purchase #3 $84.96   12.321%   $95.4279   $95.43   $95.45   $95.40  
  Purchase #4 $221.57   12.427%   $249.1045   $249.10   $249.10   $249.10  
  Purchase #5 $43.27   5.502%   $45.6507   $45.65   $45.65   $45.70  
  Purchase #6 $70.46   6.511%   $75.0477   $75.05   $75.05   $75.00  
  Purchase #7 $124.45   12.116%   $139.5284   $139.53   $139.55   $139.50  
  7 purchase totals = $772.13       $860.6524   $860.65   $860.70   $860.60