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 $246.96   7.323%   $265.0449   $265.04   $265.05   $265.00  
  Purchase #2 $59.79   12.409%   $67.2093   $67.21   $67.20   $67.20  
  Purchase #3 $155.89   3.318%   $161.0624   $161.06   $161.05   $161.10  
  Purchase #4 $105.44   10.558%   $116.5724   $116.57   $116.55   $116.60  
  Purchase #5 $191.36   8.186%   $207.0247   $207.02   $207.00   $207.00  
  Purchase #6 $151.59   7.668%   $163.2139   $163.21   $163.20   $163.20  
  Purchase #7 $185.36   7.455%   $199.1786   $199.18   $199.20   $199.20  
  7 purchase totals = $1,096.39       $1,179.3062   $1,179.29   $1,179.25   $1,179.30