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 $206.79   13.664%   $235.0458   $235.05   $235.05   $235.00  
  Purchase #2 $48.79   8.487%   $52.9308   $52.93   $52.95   $52.90  
  Purchase #3 $96.56   11.280%   $107.452   $107.45   $107.45   $107.50  
  Purchase #4 $233.62   6.364%   $248.4876   $248.49   $248.50   $248.50  
  Purchase #5 $68.69   5.520%   $72.4817   $72.48   $72.50   $72.50  
  Purchase #6 $186.32   8.300%   $201.7846   $201.78   $201.80   $201.80  
  Purchase #7 $69.73   4.701%   $73.008   $73.01   $73.00   $73.00  
  7 purchase totals = $910.50       $991.1905   $991.19   $991.25   $991.20