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 $39.25   10.388%   $43.3273   $43.33   $43.35   $43.30  
  Purchase #2 $47.45   4.696%   $49.6783   $49.68   $49.70   $49.70  
  Purchase #3 $249.72   9.282%   $272.899   $272.90   $272.90   $272.90  
  Purchase #4 $201.48   3.714%   $208.963   $208.96   $208.95   $209.00  
  Purchase #5 $145.88   13.470%   $165.53   $165.53   $165.55   $165.50  
  Purchase #6 $162.99   9.540%   $178.5392   $178.54   $178.55   $178.50  
  Purchase #7 $146.67   7.630%   $157.8609   $157.86   $157.85   $157.90  
  7 purchase totals = $993.44       $1,076.7977   $1,076.80   $1,076.85   $1,076.80