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 $193.42   5.564%   $204.1819   $204.18   $204.20   $204.20  
  Purchase #2 $240.53   13.771%   $273.6534   $273.65   $273.65   $273.70  
  Purchase #3 $131.90   9.330%   $144.2063   $144.21   $144.20   $144.20  
  Purchase #4 $242.52   9.810%   $266.3112   $266.31   $266.30   $266.30  
  Purchase #5 $216.61   4.611%   $226.5979   $226.60   $226.60   $226.60  
  Purchase #6 $186.37   6.506%   $198.4952   $198.50   $198.50   $198.50  
  Purchase #7 $54.44   6.812%   $58.1485   $58.15   $58.15   $58.10  
  7 purchase totals = $1,265.79       $1,371.5944   $1,371.60   $1,371.60   $1,371.60