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 $236.27   11.254%   $262.8598   $262.86   $262.85   $262.90  
  Purchase #2 $61.46   12.194%   $68.9544   $68.95   $68.95   $69.00  
  Purchase #3 $200.47   12.708%   $225.9457   $225.95   $225.95   $225.90  
  Purchase #4 $192.25   3.771%   $199.4997   $199.50   $199.50   $199.50  
  Purchase #5 $203.49   9.596%   $223.0169   $223.02   $223.00   $223.00  
  Purchase #6 $8.65   3.577%   $8.9594   $8.96   $8.95   $9.00  
  Purchase #7 $79.55   8.464%   $86.2831   $86.28   $86.30   $86.30  
  7 purchase totals = $982.14       $1,075.5190   $1,075.52   $1,075.50   $1,075.60