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 $63.77   11.242%   $70.939   $70.94   $70.95   $70.90  
  Purchase #2 $55.25   3.429%   $57.1445   $57.14   $57.15   $57.10  
  Purchase #3 $151.27   10.392%   $166.99   $166.99   $167.00   $167.00  
  Purchase #4 $59.85   12.477%   $67.3175   $67.32   $67.30   $67.30  
  Purchase #5 $169.57   9.217%   $185.1993   $185.20   $185.20   $185.20  
  Purchase #6 $105.80   7.864%   $114.1201   $114.12   $114.10   $114.10  
  Purchase #7 $234.36   9.253%   $256.0453   $256.05   $256.05   $256.00  
  7 purchase totals = $839.87       $917.7557   $917.76   $917.75   $917.60