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 $38.66   13.848%   $44.0136   $44.01   $44.00   $44.00  
  Purchase #2 $182.93   9.521%   $200.3468   $200.35   $200.35   $200.30  
  Purchase #3 $74.25   6.286%   $78.9174   $78.92   $78.90   $78.90  
  Purchase #4 $79.63   10.598%   $88.0692   $88.07   $88.05   $88.10  
  Purchase #5 $99.94   7.566%   $107.5015   $107.50   $107.50   $107.50  
  Purchase #6 $27.30   7.443%   $29.3319   $29.33   $29.35   $29.30  
  Purchase #7 $220.77   3.461%   $228.4108   $228.41   $228.40   $228.40  
  7 purchase totals = $723.48       $776.5912   $776.59   $776.55   $776.50