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 $43.87   11.742%   $49.0212   $49.02   $49.00   $49.00  
  Purchase #2 $192.88   13.369%   $218.6661   $218.67   $218.65   $218.70  
  Purchase #3 $68.54   10.787%   $75.9334   $75.93   $75.95   $75.90  
  Purchase #4 $126.87   11.473%   $141.4258   $141.43   $141.45   $141.40  
  Purchase #5 $165.36   3.442%   $171.0517   $171.05   $171.05   $171.10  
  Purchase #6 $40.90   8.248%   $44.2734   $44.27   $44.25   $44.30  
  Purchase #7 $120.50   4.704%   $126.1683   $126.17   $126.15   $126.20  
  7 purchase totals = $758.92       $826.5399   $826.54   $826.50   $826.60