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 $62.50   10.679%   $69.1744   $69.17   $69.15   $69.20  
  Purchase #2 $62.50   10.383%   $68.9894   $68.99   $69.00   $69.00  
  Purchase #3 $156.91   8.208%   $169.7892   $169.79   $169.80   $169.80  
  Purchase #4 $35.99   3.523%   $37.2579   $37.26   $37.25   $37.30  
  Purchase #5 $250.44   13.651%   $284.6276   $284.63   $284.65   $284.60  
  Purchase #6 $89.78   3.622%   $93.0318   $93.03   $93.05   $93.00  
  Purchase #7 $235.77   13.870%   $268.4713   $268.47   $268.45   $268.50  
  7 purchase totals = $893.89       $991.3416   $991.34   $991.35   $991.40