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 $77.66   10.643%   $85.9254   $85.93   $85.95   $85.90  
  Purchase #2 $130.45   13.194%   $147.6616   $147.66   $147.65   $147.70  
  Purchase #3 $148.78   4.826%   $155.9601   $155.96   $155.95   $156.00  
  Purchase #4 $82.37   4.731%   $86.2669   $86.27   $86.25   $86.30  
  Purchase #5 $175.46   6.764%   $187.3281   $187.33   $187.35   $187.30  
  Purchase #6 $148.65   12.108%   $166.6485   $166.65   $166.65   $166.60  
  Purchase #7 $15.54   10.540%   $17.1779   $17.18   $17.20   $17.20  
  7 purchase totals = $778.91       $846.9685   $846.98   $847.00   $847.00