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 $242.67   11.147%   $269.7204   $269.72   $269.70   $269.70  
  Purchase #2 $235.90   4.684%   $246.9496   $246.95   $246.95   $246.90  
  Purchase #3 $151.61   11.186%   $168.5691   $168.57   $168.55   $168.60  
  Purchase #4 $240.49   9.580%   $263.5289   $263.53   $263.55   $263.50  
  Purchase #5 $165.25   9.751%   $181.3635   $181.36   $181.35   $181.40  
  Purchase #6 $6.85   8.408%   $7.4259   $7.43   $7.45   $7.40  
  Purchase #7 $240.68   3.458%   $249.0027   $249.00   $249.00   $249.00  
  7 purchase totals = $1,283.45       $1,386.5601   $1,386.56   $1,386.55   $1,386.50