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 $69.58   10.632%   $76.9777   $76.98   $77.00   $77.00  
  Purchase #2 $236.94   11.750%   $264.7805   $264.78   $264.80   $264.80  
  Purchase #3 $249.42   11.523%   $278.1607   $278.16   $278.15   $278.20  
  Purchase #4 $175.53   4.442%   $183.327   $183.33   $183.35   $183.30  
  Purchase #5 $187.67   3.423%   $194.0939   $194.09   $194.10   $194.10  
  Purchase #6 $224.26   8.461%   $243.2346   $243.23   $243.25   $243.20  
  Purchase #7 $60.53   13.676%   $68.8081   $68.81   $68.80   $68.80  
  7 purchase totals = $1,203.93       $1,309.3825   $1,309.38   $1,309.45   $1,309.40