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 $165.28   7.219%   $177.2116   $177.21   $177.20   $177.20  
  Purchase #2 $225.28   10.253%   $248.378   $248.38   $248.40   $248.40  
  Purchase #3 $170.38   5.351%   $179.497   $179.50   $179.50   $179.50  
  Purchase #4 $215.55   7.180%   $231.0265   $231.03   $231.05   $231.00  
  Purchase #5 $110.59   8.670%   $120.1782   $120.18   $120.20   $120.20  
  Purchase #6 $114.96   4.574%   $120.2183   $120.22   $120.20   $120.20  
  Purchase #7 $133.79   13.561%   $151.9333   $151.93   $151.95   $151.90  
  7 purchase totals = $1,135.83       $1,228.4429   $1,228.45   $1,228.50   $1,228.40