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 $65.84   12.363%   $73.9798   $73.98   $74.00   $74.00  
  Purchase #2 $98.26   9.272%   $107.3707   $107.37   $107.35   $107.40  
  Purchase #3 $147.44   11.372%   $164.2069   $164.21   $164.20   $164.20  
  Purchase #4 $37.66   3.287%   $38.8979   $38.90   $38.90   $38.90  
  Purchase #5 $7.32   12.583%   $8.2411   $8.24   $8.25   $8.20  
  Purchase #6 $149.97   9.671%   $164.4736   $164.47   $164.45   $164.50  
  Purchase #7 $220.76   8.640%   $239.8337   $239.83   $239.85   $239.80  
  7 purchase totals = $727.25       $797.0037   $797.00   $797.00   $797.00