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 $223.56   8.805%   $243.2445   $243.24   $243.25   $243.20  
  Purchase #2 $54.98   3.105%   $56.6871   $56.69   $56.70   $56.70  
  Purchase #3 $130.93   11.439%   $145.9071   $145.91   $145.90   $145.90  
  Purchase #4 $183.54   10.777%   $203.3201   $203.32   $203.30   $203.30  
  Purchase #5 $244.51   13.549%   $277.6387   $277.64   $277.65   $277.60  
  Purchase #6 $92.70   5.691%   $97.9756   $97.98   $98.00   $98.00  
  Purchase #7 $22.37   9.823%   $24.5674   $24.57   $24.55   $24.60  
  7 purchase totals = $952.59       $1,049.3405   $1,049.35   $1,049.35   $1,049.30