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 $7.43   4.627%   $7.7738   $7.77   $7.75   $7.80  
  Purchase #2 $20.83   10.386%   $22.9934   $22.99   $23.00   $23.00  
  Purchase #3 $213.89   3.230%   $220.7986   $220.80   $220.80   $220.80  
  Purchase #4 $171.84   6.349%   $182.7501   $182.75   $182.75   $182.80  
  Purchase #5 $73.30   5.286%   $77.1746   $77.17   $77.15   $77.20  
  Purchase #6 $140.48   11.416%   $156.5172   $156.52   $156.50   $156.50  
  Purchase #7 $13.91   3.185%   $14.353   $14.35   $14.35   $14.40  
  7 purchase totals = $641.68       $682.3607   $682.35   $682.30   $682.50