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 $80.77   5.565%   $85.2649   $85.26   $85.25   $85.30  
  Purchase #2 $237.37   5.511%   $250.4515   $250.45   $250.45   $250.50  
  Purchase #3 $208.31   8.869%   $226.785   $226.79   $226.80   $226.80  
  Purchase #4 $155.51   3.599%   $161.1068   $161.11   $161.10   $161.10  
  Purchase #5 $119.75   6.219%   $127.1973   $127.20   $127.20   $127.20  
  Purchase #6 $229.52   5.577%   $242.3203   $242.32   $242.30   $242.30  
  Purchase #7 $21.80   4.493%   $22.7795   $22.78   $22.80   $22.80  
  7 purchase totals = $1,053.03       $1,115.9053   $1,115.91   $1,115.90   $1,116.00