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 $161.37   3.326%   $166.7372   $166.74   $166.75   $166.70  
  Purchase #2 $116.36   12.213%   $130.571   $130.57   $130.55   $130.60  
  Purchase #3 $119.86   5.765%   $126.7699   $126.77   $126.75   $126.80  
  Purchase #4 $211.92   3.172%   $218.6421   $218.64   $218.65   $218.60  
  Purchase #5 $126.91   11.133%   $141.0389   $141.04   $141.05   $141.00  
  Purchase #6 $187.77   13.246%   $212.642   $212.64   $212.65   $212.60  
  Purchase #7 $9.80   7.574%   $10.5423   $10.54   $10.55   $10.50  
  7 purchase totals = $933.99       $1,006.9434   $1,006.94   $1,006.95   $1,006.80