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 $244.88   8.443%   $265.5552   $265.56   $265.55   $265.60  
  Purchase #2 $45.25   4.683%   $47.3691   $47.37   $47.35   $47.40  
  Purchase #3 $139.39   7.809%   $150.275   $150.28   $150.30   $150.30  
  Purchase #4 $122.52   3.105%   $126.3242   $126.32   $126.30   $126.30  
  Purchase #5 $96.27   9.107%   $105.0373   $105.04   $105.05   $105.00  
  Purchase #6 $50.32   11.312%   $56.0122   $56.01   $56.00   $56.00  
  Purchase #7 $240.90   8.605%   $261.6294   $261.63   $261.65   $261.60  
  7 purchase totals = $939.53       $1,012.2024   $1,012.21   $1,012.20   $1,012.20