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 $164.46   11.615%   $183.562   $183.56   $183.55   $183.60  
  Purchase #2 $121.89   3.834%   $126.5633   $126.56   $126.55   $126.60  
  Purchase #3 $42.88   4.524%   $44.8199   $44.82   $44.80   $44.80  
  Purchase #4 $197.53   4.153%   $205.7334   $205.73   $205.75   $205.70  
  Purchase #5 $86.38   9.158%   $94.2907   $94.29   $94.30   $94.30  
  Purchase #6 $160.60   4.376%   $167.6279   $167.63   $167.65   $167.60  
  Purchase #7 $207.78   4.636%   $217.4127   $217.41   $217.40   $217.40  
  7 purchase totals = $981.52       $1,040.0099   $1,040.00   $1,040.00   $1,040.00