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 $237.89   12.438%   $267.4788   $267.48   $267.50   $267.50  
  Purchase #2 $43.26   8.688%   $47.0184   $47.02   $47.00   $47.00  
  Purchase #3 $195.59   12.874%   $220.7703   $220.77   $220.75   $220.80  
  Purchase #4 $11.77   6.648%   $12.5525   $12.55   $12.55   $12.60  
  Purchase #5 $163.42   11.174%   $181.6806   $181.68   $181.70   $181.70  
  Purchase #6 $219.38   9.305%   $239.7933   $239.79   $239.80   $239.80  
  Purchase #7 $89.70   5.194%   $94.359   $94.36   $94.35   $94.40  
  7 purchase totals = $961.01       $1,063.6529   $1,063.65   $1,063.65   $1,063.80