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 $244.79   12.684%   $275.8392   $275.84   $275.85   $275.80  
  Purchase #2 $236.26   12.736%   $266.3501   $266.35   $266.35   $266.40  
  Purchase #3 $88.54   8.842%   $96.3687   $96.37   $96.35   $96.40  
  Purchase #4 $116.93   8.573%   $126.9544   $126.95   $126.95   $127.00  
  Purchase #5 $86.64   10.703%   $95.9131   $95.91   $95.90   $95.90  
  Purchase #6 $130.28   11.789%   $145.6387   $145.64   $145.65   $145.60  
  Purchase #7 $19.83   10.452%   $21.9026   $21.90   $21.90   $21.90  
  7 purchase totals = $923.27       $1,028.9668   $1,028.96   $1,028.95   $1,029.00