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 $218.89   10.236%   $241.2956   $241.30   $241.30   $241.30  
  Purchase #2 $237.47   11.590%   $264.9928   $264.99   $265.00   $265.00  
  Purchase #3 $144.25   4.547%   $150.809   $150.81   $150.80   $150.80  
  Purchase #4 $78.73   9.704%   $86.37   $86.37   $86.35   $86.40  
  Purchase #5 $96.90   13.135%   $109.6278   $109.63   $109.65   $109.60  
  Purchase #6 $30.43   11.820%   $34.0268   $34.03   $34.05   $34.00  
  Purchase #7 $154.76   9.714%   $169.7934   $169.79   $169.80   $169.80  
  7 purchase totals = $961.43       $1,056.9154   $1,056.92   $1,056.95   $1,056.90