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 $61.95   8.412%   $67.1612   $67.16   $67.15   $67.20  
  Purchase #2 $95.26   11.840%   $106.5388   $106.54   $106.55   $106.50  
  Purchase #3 $12.45   3.519%   $12.8881   $12.89   $12.90   $12.90  
  Purchase #4 $57.69   5.579%   $60.9085   $60.91   $60.90   $60.90  
  Purchase #5 $164.64   8.483%   $178.6064   $178.61   $178.60   $178.60  
  Purchase #6 $212.84   5.245%   $224.0035   $224.00   $224.00   $224.00  
  Purchase #7 $177.62   3.216%   $183.3323   $183.33   $183.35   $183.30  
  7 purchase totals = $782.45       $833.4388   $833.44   $833.45   $833.40