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 $166.83   11.447%   $185.927   $185.93   $185.95   $185.90  
  Purchase #2 $134.33   13.415%   $152.3504   $152.35   $152.35   $152.40  
  Purchase #3 $78.98   7.167%   $84.6405   $84.64   $84.65   $84.60  
  Purchase #4 $198.40   8.656%   $215.5735   $215.57   $215.55   $215.60  
  Purchase #5 $80.28   3.661%   $83.2191   $83.22   $83.20   $83.20  
  Purchase #6 $212.77   5.843%   $225.2022   $225.20   $225.20   $225.20  
  Purchase #7 $157.38   8.750%   $171.1508   $171.15   $171.15   $171.20  
  7 purchase totals = $1,028.97       $1,118.0635   $1,118.06   $1,118.05   $1,118.10