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 $209.44   8.149%   $226.5073   $226.51   $226.50   $226.50  
  Purchase #2 $206.29   13.547%   $234.2361   $234.24   $234.25   $234.20  
  Purchase #3 $182.65   5.254%   $192.2464   $192.25   $192.25   $192.20  
  Purchase #4 $232.26   10.145%   $255.8228   $255.82   $255.80   $255.80  
  Purchase #5 $179.62   6.325%   $190.981   $190.98   $191.00   $191.00  
  Purchase #6 $163.25   7.415%   $175.355   $175.36   $175.35   $175.40  
  Purchase #7 $62.38   8.697%   $67.8052   $67.81   $67.80   $67.80  
  7 purchase totals = $1,235.89       $1,342.9538   $1,342.97   $1,342.95   $1,342.90