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 $136.54   7.381%   $146.618   $146.62   $146.60   $146.60  
  Purchase #2 $184.33   5.280%   $194.0626   $194.06   $194.05   $194.10  
  Purchase #3 $182.71   3.753%   $189.5671   $189.57   $189.55   $189.60  
  Purchase #4 $181.77   9.453%   $198.9527   $198.95   $198.95   $199.00  
  Purchase #5 $60.29   10.212%   $66.4468   $66.45   $66.45   $66.40  
  Purchase #6 $238.42   4.750%   $249.745   $249.75   $249.75   $249.70  
  Purchase #7 $115.98   3.162%   $119.6473   $119.65   $119.65   $119.60  
  7 purchase totals = $1,100.04       $1,165.0395   $1,165.05   $1,165.00   $1,165.00