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 $244.61   3.604%   $253.4257   $253.43   $253.45   $253.40  
  Purchase #2 $13.63   6.457%   $14.5101   $14.51   $14.50   $14.50  
  Purchase #3 $207.95   5.439%   $219.2604   $219.26   $219.25   $219.30  
  Purchase #4 $65.91   3.490%   $68.2103   $68.21   $68.20   $68.20  
  Purchase #5 $145.61   5.821%   $154.086   $154.09   $154.10   $154.10  
  Purchase #6 $95.82   4.126%   $99.7735   $99.77   $99.75   $99.80  
  Purchase #7 $187.68   13.697%   $213.3865   $213.39   $213.40   $213.40  
  7 purchase totals = $961.21       $1,022.6525   $1,022.66   $1,022.65   $1,022.70