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	$68.31	6.721%	$72.9011	$72.90	$72.90	$72.90
Purchase #2	$127.44	6.617%	$135.8727	$135.87	$135.85	$135.90
Purchase #3	$225.28	3.200%	$232.489	$232.49	$232.50	$232.50
Purchase #4	$201.56	13.180%	$228.1256	$228.13	$228.15	$228.10
Purchase #5	$178.47	11.355%	$198.7353	$198.74	$198.75	$198.70
Purchase #6	$84.31	6.578%	$89.8559	$89.86	$89.85	$89.90
Purchase #7	$131.55	7.797%	$141.807	$141.81	$141.80	$141.80
7 purchase totals =	$1,016.92		$1,099.7866	$1,099.80	$1,099.80	$1,099.80