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 $186.50   10.291%   $205.6927   $205.69   $205.70   $205.70  
  Purchase #2 $21.28   12.108%   $23.8566   $23.86   $23.85   $23.90  
  Purchase #3 $150.32   6.104%   $159.4955   $159.50   $159.50   $159.50  
  Purchase #4 $217.94   6.633%   $232.396   $232.40   $232.40   $232.40  
  Purchase #5 $130.92   3.719%   $135.7889   $135.79   $135.80   $135.80  
  Purchase #6 $245.48   12.851%   $277.0266   $277.03   $277.05   $277.00  
  Purchase #7 $107.64   3.189%   $111.0726   $111.07   $111.05   $111.10  
  7 purchase totals = $1,060.08       $1,145.3289   $1,145.34   $1,145.35   $1,145.40