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 $70.82   7.683%   $76.2611   $76.26   $76.25   $76.30  
  Purchase #2 $221.36   12.871%   $249.8512   $249.85   $249.85   $249.90  
  Purchase #3 $241.80   11.298%   $269.1186   $269.12   $269.10   $269.10  
  Purchase #4 $94.92   12.542%   $106.8249   $106.82   $106.80   $106.80  
  Purchase #5 $114.67   12.707%   $129.2411   $129.24   $129.25   $129.20  
  Purchase #6 $223.33   13.578%   $253.6537   $253.65   $253.65   $253.70  
  Purchase #7 $224.79   6.209%   $238.7472   $238.75   $238.75   $238.70  
  7 purchase totals = $1,191.69       $1,323.6978   $1,323.69   $1,323.65   $1,323.70