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 $44.98   9.632%   $49.3125   $49.31   $49.30   $49.30  
  Purchase #2 $213.50   10.820%   $236.6007   $236.60   $236.60   $236.60  
  Purchase #3 $150.72   7.423%   $161.9079   $161.91   $161.90   $161.90  
  Purchase #4 $218.91   3.426%   $226.4099   $226.41   $226.40   $226.40  
  Purchase #5 $28.55   6.749%   $30.4768   $30.48   $30.50   $30.50  
  Purchase #6 $9.43   8.850%   $10.2646   $10.26   $10.25   $10.30  
  Purchase #7 $30.33   4.824%   $31.7931   $31.79   $31.80   $31.80  
  7 purchase totals = $696.42       $746.7655   $746.76   $746.75   $746.80