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 $58.62   6.133%   $62.2152   $62.22   $62.20   $62.20  
  Purchase #2 $111.28   3.801%   $115.5098   $115.51   $115.50   $115.50  
  Purchase #3 $59.59   3.615%   $61.7442   $61.74   $61.75   $61.70  
  Purchase #4 $229.69   13.290%   $260.2158   $260.22   $260.20   $260.20  
  Purchase #5 $223.39   10.223%   $246.2272   $246.23   $246.25   $246.20  
  Purchase #6 $114.48   7.649%   $123.2366   $123.24   $123.25   $123.20  
  Purchase #7 $23.65   5.542%   $24.9607   $24.96   $24.95   $25.00  
  7 purchase totals = $820.70       $894.1095   $894.12   $894.10   $894.00