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	$19.55	9.727%	$21.4516	$21.45	$21.45	$21.50
Purchase #2	$93.82	10.221%	$103.4093	$103.41	$103.40	$103.40
Purchase #3	$165.48	12.686%	$186.4728	$186.47	$186.45	$186.50
Purchase #4	$201.35	4.621%	$210.6544	$210.65	$210.65	$210.70
Purchase #5	$82.83	8.683%	$90.0221	$90.02	$90.00	$90.00
Purchase #6	$84.82	11.360%	$94.4556	$94.46	$94.45	$94.50
Purchase #7	$36.57	7.394%	$39.274	$39.27	$39.25	$39.30
7 purchase totals =	$684.42		$745.7398	$745.73	$745.65	$745.90