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 $76.66   12.557%   $86.2862   $86.29   $86.30   $86.30  
  Purchase #2 $80.53   8.795%   $87.6126   $87.61   $87.60   $87.60  
  Purchase #3 $198.79   5.454%   $209.632   $209.63   $209.65   $209.60  
  Purchase #4 $119.90   3.420%   $124.0006   $124.00   $124.00   $124.00  
  Purchase #5 $218.81   6.221%   $232.4222   $232.42   $232.40   $232.40  
  Purchase #6 $90.65   10.458%   $100.1302   $100.13   $100.15   $100.10  
  Purchase #7 $148.25   3.174%   $152.9555   $152.96   $152.95   $153.00  
  7 purchase totals = $933.59       $993.0393   $993.04   $993.05   $993.00