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 $248.53   4.476%   $259.6542   $259.65   $259.65   $259.70  
  Purchase #2 $118.50   7.132%   $126.9514   $126.95   $126.95   $127.00  
  Purchase #3 $116.77   9.374%   $127.716   $127.72   $127.70   $127.70  
  Purchase #4 $59.47   9.392%   $65.0554   $65.06   $65.05   $65.10  
  Purchase #5 $78.79   6.740%   $84.1004   $84.10   $84.10   $84.10  
  Purchase #6 $169.27   13.492%   $192.1079   $192.11   $192.10   $192.10  
  Purchase #7 $58.64   4.502%   $61.28   $61.28   $61.30   $61.30  
  7 purchase totals = $849.97       $916.8653   $916.87   $916.85   $917.00