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 $61.93   9.734%   $67.9583   $67.96   $67.95   $68.00  
  Purchase #2 $185.65   13.278%   $210.3006   $210.30   $210.30   $210.30  
  Purchase #3 $81.93   3.195%   $84.5477   $84.55   $84.55   $84.50  
  Purchase #4 $120.86   10.379%   $133.4041   $133.40   $133.40   $133.40  
  Purchase #5 $144.99   10.516%   $160.2371   $160.24   $160.25   $160.20  
  Purchase #6 $73.99   10.730%   $81.9291   $81.93   $81.95   $81.90  
  Purchase #7 $139.47   5.516%   $147.1632   $147.16   $147.15   $147.20  
  7 purchase totals = $808.82       $885.5401   $885.54   $885.55   $885.50