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 $89.86   10.707%   $99.4813   $99.48   $99.50   $99.50  
  Purchase #2 $221.61   8.148%   $239.6668   $239.67   $239.65   $239.70  
  Purchase #3 $82.95   4.314%   $86.5285   $86.53   $86.55   $86.50  
  Purchase #4 $204.78   13.784%   $233.0069   $233.01   $233.00   $233.00  
  Purchase #5 $185.92   13.376%   $210.7887   $210.79   $210.80   $210.80  
  Purchase #6 $107.53   10.636%   $118.9669   $118.97   $118.95   $119.00  
  Purchase #7 $182.60   6.481%   $194.4343   $194.43   $194.45   $194.40  
  7 purchase totals = $1,075.25       $1,182.8734   $1,182.88   $1,182.90   $1,182.90