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 $126.26   12.312%   $141.8051   $141.81   $141.80   $141.80  
  Purchase #2 $147.42   11.470%   $164.3291   $164.33   $164.35   $164.30  
  Purchase #3 $61.58   7.286%   $66.0667   $66.07   $66.05   $66.10  
  Purchase #4 $236.65   6.399%   $251.7932   $251.79   $251.80   $251.80  
  Purchase #5 $17.85   7.258%   $19.1456   $19.15   $19.15   $19.10  
  Purchase #6 $166.55   13.109%   $188.383   $188.38   $188.40   $188.40  
  Purchase #7 $66.44   10.568%   $73.4614   $73.46   $73.45   $73.50  
  7 purchase totals = $822.75       $904.9841   $904.99   $905.00   $905.00