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 $30.76   4.717%   $32.2109   $32.21   $32.20   $32.20  
  Purchase #2 $216.58   13.149%   $245.0581   $245.06   $245.05   $245.10  
  Purchase #3 $167.49   10.211%   $184.5924   $184.59   $184.60   $184.60  
  Purchase #4 $161.65   11.727%   $180.6067   $180.61   $180.60   $180.60  
  Purchase #5 $32.60   6.359%   $34.673   $34.67   $34.65   $34.70  
  Purchase #6 $196.97   12.140%   $220.8822   $220.88   $220.90   $220.90  
  Purchase #7 $143.61   5.778%   $151.9078   $151.91   $151.90   $151.90  
  7 purchase totals = $949.66       $1,049.9311   $1,049.93   $1,049.90   $1,050.00