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 $219.90   12.457%   $247.2929   $247.29   $247.30   $247.30  
  Purchase #2 $127.98   9.179%   $139.7273   $139.73   $139.75   $139.70  
  Purchase #3 $19.91   5.689%   $21.0427   $21.04   $21.05   $21.00  
  Purchase #4 $116.64   4.278%   $121.6299   $121.63   $121.65   $121.60  
  Purchase #5 $30.74   13.309%   $34.8312   $34.83   $34.85   $34.80  
  Purchase #6 $212.92   6.854%   $227.5135   $227.51   $227.50   $227.50  
  Purchase #7 $218.27   12.802%   $246.2129   $246.21   $246.20   $246.20  
  7 purchase totals = $946.36       $1,038.2504   $1,038.24   $1,038.30   $1,038.10