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 $136.85   3.228%   $141.2675   $141.27   $141.25   $141.30  
  Purchase #2 $229.71   9.569%   $251.6909   $251.69   $251.70   $251.70  
  Purchase #3 $132.42   7.702%   $142.619   $142.62   $142.60   $142.60  
  Purchase #4 $237.83   6.221%   $252.6254   $252.63   $252.65   $252.60  
  Purchase #5 $165.97   3.269%   $171.3956   $171.40   $171.40   $171.40  
  Purchase #6 $220.56   7.220%   $236.4844   $236.48   $236.50   $236.50  
  Purchase #7 $145.89   3.499%   $150.9947   $150.99   $151.00   $151.00  
  7 purchase totals = $1,269.23       $1,347.0775   $1,347.08   $1,347.10   $1,347.10