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 $24.48   8.327%   $26.5184   $26.52   $26.50   $26.50  
  Purchase #2 $208.83   9.439%   $228.5415   $228.54   $228.55   $228.50  
  Purchase #3 $183.91   4.759%   $192.6623   $192.66   $192.65   $192.70  
  Purchase #4 $62.27   13.202%   $70.4909   $70.49   $70.50   $70.50  
  Purchase #5 $14.85   8.749%   $16.1492   $16.15   $16.15   $16.10  
  Purchase #6 $99.77   10.363%   $110.1092   $110.11   $110.10   $110.10  
  Purchase #7 $71.89   3.394%   $74.3299   $74.33   $74.35   $74.30  
  7 purchase totals = $666.00       $718.8014   $718.80   $718.80   $718.70