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 $238.32   12.102%   $267.1615   $267.16   $267.15   $267.20  
  Purchase #2 $185.58   4.194%   $193.3632   $193.36   $193.35   $193.40  
  Purchase #3 $37.75   9.663%   $41.3978   $41.40   $41.40   $41.40  
  Purchase #4 $244.53   6.583%   $260.6274   $260.63   $260.65   $260.60  
  Purchase #5 $172.76   5.228%   $181.7919   $181.79   $181.80   $181.80  
  Purchase #6 $42.92   3.468%   $44.4085   $44.41   $44.40   $44.40  
  Purchase #7 $53.58   3.626%   $55.5228   $55.52   $55.50   $55.50  
  7 purchase totals = $975.44       $1,044.2731   $1,044.27   $1,044.25   $1,044.30