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 $161.77   6.570%   $172.3983   $172.40   $172.40   $172.40  
  Purchase #2 $238.51   4.767%   $249.8798   $249.88   $249.90   $249.90  
  Purchase #3 $74.88   10.194%   $82.5133   $82.51   $82.50   $82.50  
  Purchase #4 $54.92   12.734%   $61.9135   $61.91   $61.90   $61.90  
  Purchase #5 $117.45   3.603%   $121.6817   $121.68   $121.70   $121.70  
  Purchase #6 $23.45   13.521%   $26.6207   $26.62   $26.60   $26.60  
  Purchase #7 $190.58   7.144%   $204.195   $204.20   $204.20   $204.20  
  7 purchase totals = $861.56       $919.2023   $919.20   $919.20   $919.20