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 $120.89   8.806%   $131.5356   $131.54   $131.55   $131.50  
  Purchase #2 $186.94   8.513%   $202.8542   $202.85   $202.85   $202.90  
  Purchase #3 $198.98   4.797%   $208.5251   $208.53   $208.55   $208.50  
  Purchase #4 $76.44   10.728%   $84.6405   $84.64   $84.65   $84.60  
  Purchase #5 $109.45   12.358%   $122.9758   $122.98   $123.00   $123.00  
  Purchase #6 $214.49   3.169%   $221.2872   $221.29   $221.30   $221.30  
  Purchase #7 $227.28   11.762%   $254.0127   $254.01   $254.00   $254.00  
  7 purchase totals = $1,134.47       $1,225.8311   $1,225.84   $1,225.90   $1,225.80