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 $169.59   4.263%   $176.8196   $176.82   $176.80   $176.80  
  Purchase #2 $41.96   10.138%   $46.2139   $46.21   $46.20   $46.20  
  Purchase #3 $186.81   12.222%   $209.6419   $209.64   $209.65   $209.60  
  Purchase #4 $115.68   3.551%   $119.7878   $119.79   $119.80   $119.80  
  Purchase #5 $107.45   12.534%   $120.9178   $120.92   $120.90   $120.90  
  Purchase #6 $176.34   10.574%   $194.9862   $194.99   $195.00   $195.00  
  Purchase #7 $70.70   8.439%   $76.6664   $76.67   $76.65   $76.70  
  7 purchase totals = $868.53       $945.0336   $945.04   $945.00   $945.00