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 $59.76   9.863%   $65.6541   $65.65   $65.65   $65.70  
  Purchase #2 $242.74   11.553%   $270.7838   $270.78   $270.80   $270.80  
  Purchase #3 $166.66   10.562%   $184.2626   $184.26   $184.25   $184.30  
  Purchase #4 $43.92   13.805%   $49.9832   $49.98   $50.00   $50.00  
  Purchase #5 $109.82   9.310%   $120.0442   $120.04   $120.05   $120.00  
  Purchase #6 $223.61   9.177%   $244.1307   $244.13   $244.15   $244.10  
  Purchase #7 $80.64   7.729%   $86.8727   $86.87   $86.85   $86.90  
  7 purchase totals = $927.15       $1,021.7313   $1,021.71   $1,021.75   $1,021.80