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 $233.83   3.214%   $241.3453   $241.35   $241.35   $241.30  
  Purchase #2 $187.91   7.393%   $201.8022   $201.80   $201.80   $201.80  
  Purchase #3 $44.36   10.467%   $49.0032   $49.00   $49.00   $49.00  
  Purchase #4 $146.69   4.559%   $153.3776   $153.38   $153.40   $153.40  
  Purchase #5 $242.71   10.832%   $269.0003   $269.00   $269.00   $269.00  
  Purchase #6 $129.43   4.110%   $134.7496   $134.75   $134.75   $134.70  
  Purchase #7 $152.72   5.270%   $160.7683   $160.77   $160.75   $160.80  
  7 purchase totals = $1,137.65       $1,210.0465   $1,210.05   $1,210.05   $1,210.00