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 $61.27   10.158%   $67.4938   $67.49   $67.50   $67.50  
  Purchase #2 $183.41   6.304%   $194.9722   $194.97   $194.95   $195.00  
  Purchase #3 $220.32   3.307%   $227.606   $227.61   $227.60   $227.60  
  Purchase #4 $93.57   12.691%   $105.445   $105.45   $105.45   $105.40  
  Purchase #5 $5.41   6.248%   $5.748   $5.75   $5.75   $5.70  
  Purchase #6 $224.38   5.155%   $235.9468   $235.95   $235.95   $235.90  
  Purchase #7 $63.79   12.452%   $71.7331   $71.73   $71.75   $71.70  
  7 purchase totals = $852.15       $908.9449   $908.95   $908.95   $908.80