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 $230.76   4.671%   $241.5388   $241.54   $241.55   $241.50  
  Purchase #2 $43.58   11.118%   $48.4252   $48.43   $48.45   $48.40  
  Purchase #3 $45.40   4.823%   $47.5896   $47.59   $47.60   $47.60  
  Purchase #4 $115.34   6.379%   $122.6975   $122.70   $122.70   $122.70  
  Purchase #5 $26.44   13.143%   $29.915   $29.92   $29.90   $29.90  
  Purchase #6 $237.34   6.191%   $252.0337   $252.03   $252.05   $252.00  
  Purchase #7 $115.60   9.769%   $126.893   $126.89   $126.90   $126.90  
  7 purchase totals = $814.46       $869.0928   $869.10   $869.15   $869.00