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 $46.89   6.621%   $49.9946   $49.99   $50.00   $50.00  
  Purchase #2 $182.97   7.483%   $196.6616   $196.66   $196.65   $196.70  
  Purchase #3 $223.43   5.168%   $234.9769   $234.98   $235.00   $235.00  
  Purchase #4 $152.49   11.760%   $170.4228   $170.42   $170.40   $170.40  
  Purchase #5 $79.83   5.421%   $84.1576   $84.16   $84.15   $84.20  
  Purchase #6 $85.27   7.627%   $91.7735   $91.77   $91.75   $91.80  
  Purchase #7 $166.91   6.203%   $177.2634   $177.26   $177.25   $177.30  
  7 purchase totals = $937.79       $1,005.2504   $1,005.24   $1,005.20   $1,005.40