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 $24.26   10.658%   $26.8456   $26.85   $26.85   $26.80  
  Purchase #2 $165.30   6.587%   $176.1883   $176.19   $176.20   $176.20  
  Purchase #3 $137.36   10.194%   $151.3625   $151.36   $151.35   $151.40  
  Purchase #4 $238.93   10.769%   $264.6604   $264.66   $264.65   $264.70  
  Purchase #5 $56.78   6.627%   $60.5428   $60.54   $60.55   $60.50  
  Purchase #6 $22.94   5.202%   $24.1333   $24.13   $24.15   $24.10  
  Purchase #7 $160.47   7.856%   $173.0765   $173.08   $173.10   $173.10  
  7 purchase totals = $806.04       $876.8094   $876.81   $876.85   $876.80