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 $48.65   8.802%   $52.9322   $52.93   $52.95   $52.90  
  Purchase #2 $218.49   9.831%   $239.9698   $239.97   $239.95   $240.00  
  Purchase #3 $203.28   9.693%   $222.9839   $222.98   $223.00   $223.00  
  Purchase #4 $40.74   7.175%   $43.6631   $43.66   $43.65   $43.70  
  Purchase #5 $167.39   5.131%   $175.9788   $175.98   $176.00   $176.00  
  Purchase #6 $196.38   4.397%   $205.0148   $205.01   $205.00   $205.00  
  Purchase #7 $57.46   10.296%   $63.3761   $63.38   $63.40   $63.40  
  7 purchase totals = $932.39       $1,003.9187   $1,003.91   $1,003.95   $1,004.00