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 $29.87   13.814%   $33.9962   $34.00   $34.00   $34.00  
  Purchase #2 $151.58   8.357%   $164.2475   $164.25   $164.25   $164.20  
  Purchase #3 $43.71   10.470%   $48.2864   $48.29   $48.30   $48.30  
  Purchase #4 $203.68   12.637%   $229.419   $229.42   $229.40   $229.40  
  Purchase #5 $208.55   6.200%   $221.4801   $221.48   $221.50   $221.50  
  Purchase #6 $186.35   12.589%   $209.8096   $209.81   $209.80   $209.80  
  Purchase #7 $172.31   11.690%   $192.453   $192.45   $192.45   $192.50  
  7 purchase totals = $996.05       $1,099.6918   $1,099.70   $1,099.70   $1,099.70