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 $33.53   12.278%   $37.6468   $37.65   $37.65   $37.60  
  Purchase #2 $170.67   10.244%   $188.1534   $188.15   $188.15   $188.20  
  Purchase #3 $140.93   10.390%   $155.5726   $155.57   $155.55   $155.60  
  Purchase #4 $19.77   12.636%   $22.2681   $22.27   $22.25   $22.30  
  Purchase #5 $152.81   6.521%   $162.7747   $162.77   $162.75   $162.80  
  Purchase #6 $228.42   3.416%   $236.2228   $236.22   $236.20   $236.20  
  Purchase #7 $226.34   9.585%   $248.0347   $248.03   $248.05   $248.00  
  7 purchase totals = $972.47       $1,050.6731   $1,050.66   $1,050.60   $1,050.70