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 $11.65   10.595%   $12.8843   $12.88   $12.90   $12.90  
  Purchase #2 $208.79   12.463%   $234.8115   $234.81   $234.80   $234.80  
  Purchase #3 $57.97   12.683%   $65.3223   $65.32   $65.30   $65.30  
  Purchase #4 $52.70   4.245%   $54.9371   $54.94   $54.95   $54.90  
  Purchase #5 $216.74   7.734%   $233.5027   $233.50   $233.50   $233.50  
  Purchase #6 $7.36   13.158%   $8.3284   $8.33   $8.35   $8.30  
  Purchase #7 $191.30   9.635%   $209.7318   $209.73   $209.75   $209.70  
  7 purchase totals = $746.51       $819.5181   $819.51   $819.55   $819.40