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 $167.64   5.109%   $176.2047   $176.20   $176.20   $176.20  
  Purchase #2 $71.54   11.458%   $79.7371   $79.74   $79.75   $79.70  
  Purchase #3 $175.42   10.165%   $193.2514   $193.25   $193.25   $193.30  
  Purchase #4 $234.49   12.403%   $263.5738   $263.57   $263.55   $263.60  
  Purchase #5 $172.25   13.794%   $196.0102   $196.01   $196.00   $196.00  
  Purchase #6 $213.50   9.721%   $234.2543   $234.25   $234.25   $234.30  
  Purchase #7 $55.73   4.621%   $58.3053   $58.31   $58.30   $58.30  
  7 purchase totals = $1,090.57       $1,201.3368   $1,201.33   $1,201.30   $1,201.40