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	$89.66	11.658%	$100.1126	$100.11	$100.10	$100.10
Purchase #2	$39.91	10.439%	$44.0762	$44.08	$44.10	$44.10
Purchase #3	$214.48	13.738%	$243.9453	$243.95	$243.95	$243.90
Purchase #4	$135.31	6.535%	$144.1525	$144.15	$144.15	$144.20
Purchase #5	$159.77	11.808%	$178.6356	$178.64	$178.65	$178.60
Purchase #6	$162.34	3.796%	$168.5024	$168.50	$168.50	$168.50
Purchase #7	$54.43	9.780%	$59.7533	$59.75	$59.75	$59.80
7 purchase totals =	$855.90		$939.1779	$939.18	$939.20	$939.20