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 $106.55   8.221%   $115.3095   $115.31   $115.30   $115.30  
  Purchase #2 $209.81   11.587%   $234.1207   $234.12   $234.10   $234.10  
  Purchase #3 $35.37   12.217%   $39.6912   $39.69   $39.70   $39.70  
  Purchase #4 $195.39   12.769%   $220.3393   $220.34   $220.35   $220.30  
  Purchase #5 $35.33   6.861%   $37.754   $37.75   $37.75   $37.80  
  Purchase #6 $177.27   4.719%   $185.6354   $185.64   $185.65   $185.60  
  Purchase #7 $48.48   4.150%   $50.4919   $50.49   $50.50   $50.50  
  7 purchase totals = $808.20       $883.3420   $883.34   $883.35   $883.30