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 $208.89   4.425%   $218.1334   $218.13   $218.15   $218.10  
  Purchase #2 $54.76   5.829%   $57.952   $57.95   $57.95   $58.00  
  Purchase #3 $73.44   5.628%   $77.5732   $77.57   $77.55   $77.60  
  Purchase #4 $136.95   7.819%   $147.6581   $147.66   $147.65   $147.70  
  Purchase #5 $22.91   11.648%   $25.5786   $25.58   $25.60   $25.60  
  Purchase #6 $101.77   10.479%   $112.4345   $112.43   $112.45   $112.40  
  Purchase #7 $137.60   5.159%   $144.6988   $144.70   $144.70   $144.70  
  7 purchase totals = $736.32       $784.0286   $784.02   $784.05   $784.10