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 $225.76   6.862%   $241.2517   $241.25   $241.25   $241.30  
  Purchase #2 $120.97   11.219%   $134.5416   $134.54   $134.55   $134.50  
  Purchase #3 $244.27   6.322%   $259.7127   $259.71   $259.70   $259.70  
  Purchase #4 $52.75   7.296%   $56.5986   $56.60   $56.60   $56.60  
  Purchase #5 $85.88   8.473%   $93.1566   $93.16   $93.15   $93.20  
  Purchase #6 $231.84   5.808%   $245.3053   $245.31   $245.30   $245.30  
  Purchase #7 $143.80   12.426%   $161.6686   $161.67   $161.65   $161.70  
  7 purchase totals = $1,105.27       $1,192.2351   $1,192.24   $1,192.20   $1,192.30