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 $22.83   6.461%   $24.305   $24.31   $24.30   $24.30  
  Purchase #2 $49.91   7.717%   $53.7616   $53.76   $53.75   $53.80  
  Purchase #3 $61.59   7.146%   $65.9912   $65.99   $66.00   $66.00  
  Purchase #4 $53.68   5.167%   $56.4536   $56.45   $56.45   $56.50  
  Purchase #5 $172.94   9.576%   $189.5007   $189.50   $189.50   $189.50  
  Purchase #6 $111.94   5.791%   $118.4224   $118.42   $118.40   $118.40  
  Purchase #7 $239.26   11.658%   $267.1529   $267.15   $267.15   $267.20  
  7 purchase totals = $712.15       $775.5874   $775.58   $775.55   $775.70