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 $162.87   5.719%   $172.1845   $172.18   $172.20   $172.20  
  Purchase #2 $87.97   6.808%   $93.959   $93.96   $93.95   $94.00  
  Purchase #3 $103.93   8.649%   $112.9189   $112.92   $112.90   $112.90  
  Purchase #4 $219.80   4.305%   $229.2624   $229.26   $229.25   $229.30  
  Purchase #5 $201.36   6.390%   $214.2269   $214.23   $214.25   $214.20  
  Purchase #6 $5.81   13.712%   $6.6067   $6.61   $6.60   $6.60  
  Purchase #7 $116.40   9.843%   $127.8573   $127.86   $127.85   $127.90  
  7 purchase totals = $898.14       $957.0157   $957.02   $957.00   $957.10