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 $241.70   11.281%   $268.9662   $268.97   $268.95   $269.00  
  Purchase #2 $150.99   8.702%   $164.1291   $164.13   $164.15   $164.10  
  Purchase #3 $49.75   4.801%   $52.1385   $52.14   $52.15   $52.10  
  Purchase #4 $210.85   12.658%   $237.5394   $237.54   $237.55   $237.50  
  Purchase #5 $237.65   6.536%   $253.1828   $253.18   $253.20   $253.20  
  Purchase #6 $191.37   9.206%   $208.9875   $208.99   $209.00   $209.00  
  Purchase #7 $210.75   5.311%   $221.9429   $221.94   $221.95   $221.90  
  7 purchase totals = $1,293.06       $1,406.8864   $1,406.89   $1,406.95   $1,406.80