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 $62.71   9.241%   $68.505   $68.51   $68.50   $68.50  
  Purchase #2 $175.63   6.319%   $186.7281   $186.73   $186.75   $186.70  
  Purchase #3 $43.62   12.115%   $48.9046   $48.90   $48.90   $48.90  
  Purchase #4 $138.76   10.142%   $152.833   $152.83   $152.85   $152.80  
  Purchase #5 $67.67   10.606%   $74.8471   $74.85   $74.85   $74.80  
  Purchase #6 $192.26   10.629%   $212.6953   $212.70   $212.70   $212.70  
  Purchase #7 $53.89   6.218%   $57.2409   $57.24   $57.25   $57.20  
  7 purchase totals = $734.54       $801.7540   $801.76   $801.80   $801.60