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 $84.86   13.181%   $96.0454   $96.05   $96.05   $96.00  
  Purchase #2 $24.38   5.662%   $25.7604   $25.76   $25.75   $25.80  
  Purchase #3 $145.37   6.318%   $154.5545   $154.55   $154.55   $154.60  
  Purchase #4 $156.43   4.161%   $162.9391   $162.94   $162.95   $162.90  
  Purchase #5 $192.68   11.264%   $214.3835   $214.38   $214.40   $214.40  
  Purchase #6 $35.44   11.537%   $39.5287   $39.53   $39.55   $39.50  
  Purchase #7 $138.68   10.234%   $152.8725   $152.87   $152.85   $152.90  
  7 purchase totals = $777.84       $846.0841   $846.08   $846.10   $846.10