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 $200.92   8.677%   $218.3538   $218.35   $218.35   $218.40  
  Purchase #2 $89.95   12.341%   $101.0507   $101.05   $101.05   $101.10  
  Purchase #3 $111.53   6.683%   $118.9835   $118.98   $119.00   $119.00  
  Purchase #4 $95.93   11.732%   $107.1845   $107.18   $107.20   $107.20  
  Purchase #5 $232.80   3.720%   $241.4602   $241.46   $241.45   $241.50  
  Purchase #6 $235.67   4.233%   $245.6459   $245.65   $245.65   $245.60  
  Purchase #7 $193.38   7.709%   $208.2877   $208.29   $208.30   $208.30  
  7 purchase totals = $1,160.18       $1,240.9663   $1,240.96   $1,241.00   $1,241.10