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	$242.32	6.102%	$257.1064	$257.11	$257.10	$257.10
Purchase #2	$38.83	9.299%	$42.4408	$42.44	$42.45	$42.40
Purchase #3	$226.52	3.500%	$234.4482	$234.45	$234.45	$234.40
Purchase #4	$162.47	13.390%	$184.2247	$184.22	$184.20	$184.20
Purchase #5	$65.48	10.429%	$72.3089	$72.31	$72.30	$72.30
Purchase #6	$33.30	6.736%	$35.5431	$35.54	$35.55	$35.50
Purchase #7	$236.52	6.489%	$251.8678	$251.87	$251.85	$251.90
7 purchase totals =	$1,005.44		$1,077.9399	$1,077.94	$1,077.90	$1,077.80