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 $188.74   11.342%   $210.1469   $210.15   $210.15   $210.10  
  Purchase #2 $24.57   5.844%   $26.0059   $26.01   $26.00   $26.00  
  Purchase #3 $120.33   5.297%   $126.7039   $126.70   $126.70   $126.70  
  Purchase #4 $221.33   10.576%   $244.7379   $244.74   $244.75   $244.70  
  Purchase #5 $179.33   6.268%   $190.5704   $190.57   $190.55   $190.60  
  Purchase #6 $127.81   13.168%   $144.64   $144.64   $144.65   $144.60  
  Purchase #7 $240.43   3.153%   $248.0108   $248.01   $248.00   $248.00  
  7 purchase totals = $1,102.54       $1,190.8158   $1,190.82   $1,190.80   $1,190.70