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 $156.74   6.429%   $166.8168   $166.82   $166.80   $166.80  
  Purchase #2 $22.69   4.334%   $23.6734   $23.67   $23.65   $23.70  
  Purchase #3 $172.54   13.190%   $195.298   $195.30   $195.30   $195.30  
  Purchase #4 $159.92   10.386%   $176.5293   $176.53   $176.55   $176.50  
  Purchase #5 $208.80   3.701%   $216.5277   $216.53   $216.55   $216.50  
  Purchase #6 $95.38   8.194%   $103.1954   $103.20   $103.20   $103.20  
  Purchase #7 $88.75   5.191%   $93.357   $93.36   $93.35   $93.40  
  7 purchase totals = $904.82       $975.3976   $975.41   $975.40   $975.40