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 $24.86   7.126%   $26.6315   $26.63   $26.65   $26.60  
  Purchase #2 $10.86   6.269%   $11.5408   $11.54   $11.55   $11.50  
  Purchase #3 $80.31   4.240%   $83.7151   $83.72   $83.70   $83.70  
  Purchase #4 $212.52   7.697%   $228.8777   $228.88   $228.90   $228.90  
  Purchase #5 $170.76   8.706%   $185.6264   $185.63   $185.65   $185.60  
  Purchase #6 $203.53   8.496%   $220.8219   $220.82   $220.80   $220.80  
  Purchase #7 $42.40   6.461%   $45.1395   $45.14   $45.15   $45.10  
  7 purchase totals = $745.24       $802.3529   $802.36   $802.40   $802.20