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 $84.79   13.559%   $96.2867   $96.29   $96.30   $96.30  
  Purchase #2 $181.33   7.490%   $194.9116   $194.91   $194.90   $194.90  
  Purchase #3 $234.59   4.209%   $244.4639   $244.46   $244.45   $244.50  
  Purchase #4 $247.66   6.205%   $263.0273   $263.03   $263.05   $263.00  
  Purchase #5 $139.76   10.669%   $154.671   $154.67   $154.65   $154.70  
  Purchase #6 $52.57   6.767%   $56.1274   $56.13   $56.15   $56.10  
  Purchase #7 $9.53   4.389%   $9.9483   $9.95   $9.95   $9.90  
  7 purchase totals = $950.23       $1,019.4362   $1,019.44   $1,019.45   $1,019.40