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 $216.93   13.553%   $246.3305   $246.33   $246.35   $246.30  
  Purchase #2 $163.78   8.136%   $177.1051   $177.11   $177.10   $177.10  
  Purchase #3 $129.91   12.258%   $145.8344   $145.83   $145.85   $145.80  
  Purchase #4 $158.91   10.333%   $175.3302   $175.33   $175.35   $175.30  
  Purchase #5 $65.43   13.551%   $74.2964   $74.30   $74.30   $74.30  
  Purchase #6 $114.70   6.490%   $122.144   $122.14   $122.15   $122.10  
  Purchase #7 $67.25   3.111%   $69.3421   $69.34   $69.35   $69.30  
  7 purchase totals = $916.91       $1,010.3827   $1,010.38   $1,010.45   $1,010.20