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 $198.76   12.462%   $223.5295   $223.53   $223.55   $223.50  
  Purchase #2 $68.73   3.290%   $70.9912   $70.99   $71.00   $71.00  
  Purchase #3 $9.33   5.840%   $9.8749   $9.87   $9.85   $9.90  
  Purchase #4 $157.68   10.457%   $174.1686   $174.17   $174.15   $174.20  
  Purchase #5 $214.92   5.125%   $225.9347   $225.93   $225.95   $225.90  
  Purchase #6 $240.68   13.603%   $273.4197   $273.42   $273.40   $273.40  
  Purchase #7 $71.91   4.719%   $75.3034   $75.30   $75.30   $75.30  
  7 purchase totals = $962.01       $1,053.2220   $1,053.21   $1,053.20   $1,053.20