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 $247.62   6.432%   $263.5469   $263.55   $263.55   $263.50  
  Purchase #2 $211.81   10.866%   $234.8253   $234.83   $234.85   $234.80  
  Purchase #3 $55.61   10.743%   $61.5842   $61.58   $61.60   $61.60  
  Purchase #4 $19.45   9.612%   $21.3195   $21.32   $21.30   $21.30  
  Purchase #5 $157.61   4.640%   $164.9231   $164.92   $164.90   $164.90  
  Purchase #6 $194.57   6.821%   $207.8416   $207.84   $207.85   $207.80  
  Purchase #7 $48.31   5.604%   $51.0173   $51.02   $51.00   $51.00  
  7 purchase totals = $934.98       $1,005.0579   $1,005.06   $1,005.05   $1,004.90