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 $154.61   8.640%   $167.9683   $167.97   $167.95   $168.00  
  Purchase #2 $241.65   6.176%   $256.5743   $256.57   $256.55   $256.60  
  Purchase #3 $75.94   13.452%   $86.1554   $86.16   $86.15   $86.20  
  Purchase #4 $96.72   6.121%   $102.6402   $102.64   $102.65   $102.60  
  Purchase #5 $81.57   11.231%   $90.7311   $90.73   $90.75   $90.70  
  Purchase #6 $194.97   9.377%   $213.2523   $213.25   $213.25   $213.30  
  Purchase #7 $40.80   9.169%   $44.541   $44.54   $44.55   $44.50  
  7 purchase totals = $886.26       $961.8626   $961.86   $961.85   $961.90