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 $76.60   11.121%   $85.1187   $85.12   $85.10   $85.10  
  Purchase #2 $169.38   10.289%   $186.8075   $186.81   $186.80   $186.80  
  Purchase #3 $148.74   5.259%   $156.5622   $156.56   $156.55   $156.60  
  Purchase #4 $235.32   12.726%   $265.2668   $265.27   $265.25   $265.30  
  Purchase #5 $114.54   6.419%   $121.8923   $121.89   $121.90   $121.90  
  Purchase #6 $243.64   12.774%   $274.7626   $274.76   $274.75   $274.80  
  Purchase #7 $215.95   7.403%   $231.9368   $231.94   $231.95   $231.90  
  7 purchase totals = $1,204.17       $1,322.3469   $1,322.35   $1,322.30   $1,322.40