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 $127.71   5.421%   $134.6332   $134.63   $134.65   $134.60  
  Purchase #2 $65.78   11.277%   $73.198   $73.20   $73.20   $73.20  
  Purchase #3 $145.74   5.545%   $153.8213   $153.82   $153.80   $153.80  
  Purchase #4 $114.51   7.409%   $122.994   $122.99   $123.00   $123.00  
  Purchase #5 $13.83   3.254%   $14.28   $14.28   $14.30   $14.30  
  Purchase #6 $113.27   13.859%   $128.9681   $128.97   $128.95   $129.00  
  Purchase #7 $108.91   11.313%   $121.231   $121.23   $121.25   $121.20  
  7 purchase totals = $689.75       $749.1256   $749.12   $749.15   $749.10