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 $212.48   13.643%   $241.4686   $241.47   $241.45   $241.50  
  Purchase #2 $190.59   6.487%   $202.9536   $202.95   $202.95   $203.00  
  Purchase #3 $26.58   3.771%   $27.5823   $27.58   $27.60   $27.60  
  Purchase #4 $242.42   9.723%   $265.9905   $265.99   $266.00   $266.00  
  Purchase #5 $54.41   12.288%   $61.0959   $61.10   $61.10   $61.10  
  Purchase #6 $200.69   7.305%   $215.3504   $215.35   $215.35   $215.40  
  Purchase #7 $196.79   7.658%   $211.8602   $211.86   $211.85   $211.90  
  7 purchase totals = $1,123.96       $1,226.3015   $1,226.30   $1,226.30   $1,226.50