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 $192.74   9.703%   $211.4416   $211.44   $211.45   $211.40  
  Purchase #2 $88.95   8.295%   $96.3284   $96.33   $96.35   $96.30  
  Purchase #3 $11.97   5.308%   $12.6054   $12.61   $12.60   $12.60  
  Purchase #4 $101.55   13.505%   $115.2643   $115.26   $115.25   $115.30  
  Purchase #5 $79.80   13.198%   $90.332   $90.33   $90.35   $90.30  
  Purchase #6 $107.46   9.284%   $117.4366   $117.44   $117.45   $117.40  
  Purchase #7 $90.48   13.377%   $102.5835   $102.58   $102.60   $102.60  
  7 purchase totals = $672.95       $745.9918   $745.99   $746.05   $745.90