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 $61.52   8.275%   $66.6108   $66.61   $66.60   $66.60  
  Purchase #2 $21.77   8.273%   $23.571   $23.57   $23.55   $23.60  
  Purchase #3 $245.40   9.138%   $267.8247   $267.82   $267.80   $267.80  
  Purchase #4 $201.69   8.268%   $218.3657   $218.37   $218.35   $218.40  
  Purchase #5 $232.46   6.767%   $248.1906   $248.19   $248.20   $248.20  
  Purchase #6 $192.95   6.667%   $205.814   $205.81   $205.80   $205.80  
  Purchase #7 $200.86   3.505%   $207.9001   $207.90   $207.90   $207.90  
  7 purchase totals = $1,156.65       $1,238.2769   $1,238.27   $1,238.20   $1,238.30