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 $203.75   11.109%   $226.3846   $226.38   $226.40   $226.40  
  Purchase #2 $95.74   7.229%   $102.661   $102.66   $102.65   $102.70  
  Purchase #3 $82.71   4.684%   $86.5841   $86.58   $86.60   $86.60  
  Purchase #4 $229.94   3.621%   $238.2661   $238.27   $238.25   $238.30  
  Purchase #5 $178.59   3.566%   $184.9585   $184.96   $184.95   $185.00  
  Purchase #6 $211.68   8.749%   $230.1999   $230.20   $230.20   $230.20  
  Purchase #7 $203.51   11.512%   $226.9381   $226.94   $226.95   $226.90  
  7 purchase totals = $1,205.92       $1,295.9923   $1,295.99   $1,296.00   $1,296.10