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 $58.99   11.830%   $65.9685   $65.97   $65.95   $66.00  
  Purchase #2 $231.37   7.176%   $247.9731   $247.97   $247.95   $248.00  
  Purchase #3 $74.66   9.842%   $82.008   $82.01   $82.00   $82.00  
  Purchase #4 $151.95   9.376%   $166.1968   $166.20   $166.20   $166.20  
  Purchase #5 $172.99   9.799%   $189.9413   $189.94   $189.95   $189.90  
  Purchase #6 $145.28   8.440%   $157.5416   $157.54   $157.55   $157.50  
  Purchase #7 $64.54   9.624%   $70.7513   $70.75   $70.75   $70.80  
  7 purchase totals = $899.78       $980.3806   $980.38   $980.35   $980.40