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 $66.99   4.239%   $69.8297   $69.83   $69.85   $69.80  
  Purchase #2 $211.59   5.725%   $223.7035   $223.70   $223.70   $223.70  
  Purchase #3 $83.48   11.407%   $93.0026   $93.00   $93.00   $93.00  
  Purchase #4 $135.89   8.408%   $147.3156   $147.32   $147.30   $147.30  
  Purchase #5 $79.32   8.578%   $86.1241   $86.12   $86.10   $86.10  
  Purchase #6 $189.56   10.709%   $209.86   $209.86   $209.85   $209.90  
  Purchase #7 $226.87   3.839%   $235.5795   $235.58   $235.60   $235.60  
  7 purchase totals = $993.70       $1,065.4150   $1,065.41   $1,065.40   $1,065.40