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 $159.89   8.837%   $174.0195   $174.02   $174.00   $174.00  
  Purchase #2 $231.89   13.294%   $262.7175   $262.72   $262.70   $262.70  
  Purchase #3 $149.91   7.513%   $161.1727   $161.17   $161.15   $161.20  
  Purchase #4 $217.41   5.474%   $229.311   $229.31   $229.30   $229.30  
  Purchase #5 $6.48   6.366%   $6.8925   $6.89   $6.90   $6.90  
  Purchase #6 $117.28   3.524%   $121.4129   $121.41   $121.40   $121.40  
  Purchase #7 $222.48   13.290%   $252.0476   $252.05   $252.05   $252.00  
  7 purchase totals = $1,105.34       $1,207.5737   $1,207.57   $1,207.50   $1,207.50