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 $241.87   10.795%   $267.9799   $267.98   $268.00   $268.00  
  Purchase #2 $116.38   6.376%   $123.8004   $123.80   $123.80   $123.80  
  Purchase #3 $78.58   9.573%   $86.1025   $86.10   $86.10   $86.10  
  Purchase #4 $171.32   7.777%   $184.6436   $184.64   $184.65   $184.60  
  Purchase #5 $202.32   10.740%   $224.0492   $224.05   $224.05   $224.00  
  Purchase #6 $70.92   9.583%   $77.7163   $77.72   $77.70   $77.70  
  Purchase #7 $134.42   9.565%   $147.2773   $147.28   $147.30   $147.30  
  7 purchase totals = $1,015.81       $1,111.5692   $1,111.57   $1,111.60   $1,111.50