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	$18.61	12.673%	$20.9684	$20.97	$20.95	$21.00
Purchase #2	$167.84	7.196%	$179.9178	$179.92	$179.90	$179.90
Purchase #3	$124.43	13.139%	$140.7789	$140.78	$140.80	$140.80
Purchase #4	$51.30	11.649%	$57.2759	$57.28	$57.30	$57.30
Purchase #5	$65.78	10.643%	$72.781	$72.78	$72.80	$72.80
Purchase #6	$198.68	11.557%	$221.6414	$221.64	$221.65	$221.60
Purchase #7	$35.77	11.556%	$39.9036	$39.90	$39.90	$39.90
7 purchase totals =	$662.41		$733.2670	$733.27	$733.30	$733.30