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 $67.99   13.160%   $76.9375   $76.94   $76.95   $76.90  
  Purchase #2 $106.43   12.377%   $119.6028   $119.60   $119.60   $119.60  
  Purchase #3 $30.92   12.847%   $34.8923   $34.89   $34.90   $34.90  
  Purchase #4 $234.30   13.288%   $265.4338   $265.43   $265.45   $265.40  
  Purchase #5 $113.44   8.679%   $123.2855   $123.29   $123.30   $123.30  
  Purchase #6 $168.67   7.765%   $181.7672   $181.77   $181.75   $181.80  
  Purchase #7 $222.33   5.585%   $234.7471   $234.75   $234.75   $234.70  
  7 purchase totals = $944.08       $1,036.6662   $1,036.67   $1,036.70   $1,036.60