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 $81.46   13.365%   $92.3471   $92.35   $92.35   $92.30  
  Purchase #2 $110.62   3.435%   $114.4198   $114.42   $114.40   $114.40  
  Purchase #3 $222.73   7.639%   $239.7443   $239.74   $239.75   $239.70  
  Purchase #4 $105.63   12.556%   $118.8929   $118.89   $118.90   $118.90  
  Purchase #5 $151.70   6.613%   $161.7319   $161.73   $161.75   $161.70  
  Purchase #6 $19.72   13.793%   $22.44   $22.44   $22.45   $22.40  
  Purchase #7 $224.58   3.232%   $231.8384   $231.84   $231.85   $231.80  
  7 purchase totals = $916.44       $981.4144   $981.41   $981.45   $981.20