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 $184.83   4.197%   $192.5873   $192.59   $192.60   $192.60  
  Purchase #2 $10.99   11.136%   $12.2138   $12.21   $12.20   $12.20  
  Purchase #3 $129.48   5.381%   $136.4473   $136.45   $136.45   $136.40  
  Purchase #4 $231.95   13.243%   $262.6671   $262.67   $262.65   $262.70  
  Purchase #5 $7.96   12.648%   $8.9668   $8.97   $8.95   $9.00  
  Purchase #6 $190.67   9.544%   $208.8675   $208.87   $208.85   $208.90  
  Purchase #7 $206.33   8.513%   $223.8949   $223.89   $223.90   $223.90  
  7 purchase totals = $962.21       $1,045.6447   $1,045.65   $1,045.60   $1,045.70