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 $25.93   5.476%   $27.3499   $27.35   $27.35   $27.30  
  Purchase #2 $183.49   11.755%   $205.0592   $205.06   $205.05   $205.10  
  Purchase #3 $188.66   5.289%   $198.6382   $198.64   $198.65   $198.60  
  Purchase #4 $239.76   10.507%   $264.9516   $264.95   $264.95   $265.00  
  Purchase #5 $213.84   3.663%   $221.673   $221.67   $221.65   $221.70  
  Purchase #6 $133.53   13.630%   $151.7301   $151.73   $151.75   $151.70  
  Purchase #7 $136.99   7.336%   $147.0396   $147.04   $147.05   $147.00  
  7 purchase totals = $1,122.20       $1,216.4416   $1,216.44   $1,216.45   $1,216.40