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 $71.33   4.671%   $74.6618   $74.66   $74.65   $74.70  
  Purchase #2 $107.77   9.614%   $118.131   $118.13   $118.15   $118.10  
  Purchase #3 $57.99   6.311%   $61.6497   $61.65   $61.65   $61.60  
  Purchase #4 $65.83   6.321%   $69.9911   $69.99   $70.00   $70.00  
  Purchase #5 $144.30   13.772%   $164.173   $164.17   $164.15   $164.20  
  Purchase #6 $124.98   4.157%   $130.1754   $130.18   $130.20   $130.20  
  Purchase #7 $192.29   11.791%   $214.9629   $214.96   $214.95   $215.00  
  7 purchase totals = $764.49       $833.7449   $833.74   $833.75   $833.80