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 $61.60   3.731%   $63.8983   $63.90   $63.90   $63.90  
  Purchase #2 $141.70   11.119%   $157.4556   $157.46   $157.45   $157.50  
  Purchase #3 $203.61   7.164%   $218.1966   $218.20   $218.20   $218.20  
  Purchase #4 $173.32   12.212%   $194.4858   $194.49   $194.50   $194.50  
  Purchase #5 $215.59   4.331%   $224.9272   $224.93   $224.95   $224.90  
  Purchase #6 $247.95   4.718%   $259.6483   $259.65   $259.65   $259.60  
  Purchase #7 $149.97   11.304%   $166.9226   $166.92   $166.90   $166.90  
  7 purchase totals = $1,193.74       $1,285.5344   $1,285.55   $1,285.55   $1,285.50