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 $97.35   6.661%   $103.8345   $103.83   $103.85   $103.80  
  Purchase #2 $200.55   13.186%   $226.9945   $226.99   $227.00   $227.00  
  Purchase #3 $66.96   5.285%   $70.4988   $70.50   $70.50   $70.50  
  Purchase #4 $20.90   6.233%   $22.2027   $22.20   $22.20   $22.20  
  Purchase #5 $86.41   11.408%   $96.2677   $96.27   $96.25   $96.30  
  Purchase #6 $58.99   5.477%   $62.2209   $62.22   $62.20   $62.20  
  Purchase #7 $213.30   5.631%   $225.3109   $225.31   $225.30   $225.30  
  7 purchase totals = $744.46       $807.3300   $807.32   $807.30   $807.30