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 $153.98   7.283%   $165.1944   $165.19   $165.20   $165.20  
  Purchase #2 $230.99   12.851%   $260.6745   $260.67   $260.65   $260.70  
  Purchase #3 $6.29   9.617%   $6.8949   $6.89   $6.90   $6.90  
  Purchase #4 $52.52   10.605%   $58.0897   $58.09   $58.10   $58.10  
  Purchase #5 $173.44   12.545%   $195.198   $195.20   $195.20   $195.20  
  Purchase #6 $46.25   6.358%   $49.1906   $49.19   $49.20   $49.20  
  Purchase #7 $29.49   13.691%   $33.5275   $33.53   $33.55   $33.50  
  7 purchase totals = $692.96       $768.7696   $768.76   $768.80   $768.80