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 $63.34   12.636%   $71.3436   $71.34   $71.35   $71.30  
  Purchase #2 $192.66   7.402%   $206.9207   $206.92   $206.90   $206.90  
  Purchase #3 $246.51   9.131%   $269.0188   $269.02   $269.00   $269.00  
  Purchase #4 $127.58   13.512%   $144.8186   $144.82   $144.80   $144.80  
  Purchase #5 $105.78   11.742%   $118.2007   $118.20   $118.20   $118.20  
  Purchase #6 $178.36   8.855%   $194.1538   $194.15   $194.15   $194.20  
  Purchase #7 $243.94   4.755%   $255.5393   $255.54   $255.55   $255.50  
  7 purchase totals = $1,158.17       $1,259.9955   $1,259.99   $1,259.95   $1,259.90