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 $248.40   8.280%   $268.9675   $268.97   $268.95   $269.00  
  Purchase #2 $202.95   8.495%   $220.1906   $220.19   $220.20   $220.20  
  Purchase #3 $10.70   11.688%   $11.9506   $11.95   $11.95   $12.00  
  Purchase #4 $110.52   5.662%   $116.7776   $116.78   $116.80   $116.80  
  Purchase #5 $142.31   10.553%   $157.328   $157.33   $157.35   $157.30  
  Purchase #6 $129.64   3.102%   $133.6614   $133.66   $133.65   $133.70  
  Purchase #7 $9.57   7.526%   $10.2902   $10.29   $10.30   $10.30  
  7 purchase totals = $854.09       $919.1659   $919.17   $919.20   $919.30