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 $64.88   10.822%   $71.9013   $71.90   $71.90   $71.90  
  Purchase #2 $212.34   3.253%   $219.2474   $219.25   $219.25   $219.20  
  Purchase #3 $156.78   8.213%   $169.6563   $169.66   $169.65   $169.70  
  Purchase #4 $200.39   5.641%   $211.694   $211.69   $211.70   $211.70  
  Purchase #5 $219.80   12.535%   $247.3519   $247.35   $247.35   $247.40  
  Purchase #6 $204.61   4.576%   $213.973   $213.97   $213.95   $214.00  
  Purchase #7 $226.93   13.423%   $257.3908   $257.39   $257.40   $257.40  
  7 purchase totals = $1,285.73       $1,391.2147   $1,391.21   $1,391.20   $1,391.30