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 $183.81   12.563%   $206.9021   $206.90   $206.90   $206.90  
  Purchase #2 $200.48   10.353%   $221.2357   $221.24   $221.25   $221.20  
  Purchase #3 $82.35   13.451%   $93.4269   $93.43   $93.45   $93.40  
  Purchase #4 $155.31   4.664%   $162.5537   $162.55   $162.55   $162.60  
  Purchase #5 $154.81   7.676%   $166.6932   $166.69   $166.70   $166.70  
  Purchase #6 $55.55   5.413%   $58.5569   $58.56   $58.55   $58.60  
  Purchase #7 $95.80   5.699%   $101.2596   $101.26   $101.25   $101.30  
  7 purchase totals = $928.11       $1,010.6281   $1,010.63   $1,010.65   $1,010.70