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 $239.96   7.621%   $258.2474   $258.25   $258.25   $258.20  
  Purchase #2 $62.74   10.587%   $69.3823   $69.38   $69.40   $69.40  
  Purchase #3 $153.52   4.378%   $160.2411   $160.24   $160.25   $160.20  
  Purchase #4 $243.35   13.191%   $275.4503   $275.45   $275.45   $275.50  
  Purchase #5 $60.45   6.813%   $64.5685   $64.57   $64.55   $64.60  
  Purchase #6 $9.64   3.685%   $9.9952   $10.00   $10.00   $10.00  
  Purchase #7 $196.29   11.241%   $218.355   $218.36   $218.35   $218.40  
  7 purchase totals = $965.95       $1,056.2398   $1,056.25   $1,056.25   $1,056.30