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 $52.27   12.765%   $58.9423   $58.94   $58.95   $58.90  
  Purchase #2 $115.52   10.186%   $127.2869   $127.29   $127.30   $127.30  
  Purchase #3 $201.74   8.299%   $218.4824   $218.48   $218.50   $218.50  
  Purchase #4 $149.51   12.710%   $168.5127   $168.51   $168.50   $168.50  
  Purchase #5 $7.85   9.303%   $8.5803   $8.58   $8.60   $8.60  
  Purchase #6 $225.69   9.326%   $246.7378   $246.74   $246.75   $246.70  
  Purchase #7 $171.49   6.868%   $183.2679   $183.27   $183.25   $183.30  
  7 purchase totals = $924.07       $1,011.8103   $1,011.81   $1,011.85   $1,011.80