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	$157.67	7.691%	$169.7964	$169.80	$169.80	$169.80
Purchase #2	$32.83	9.137%	$35.8297	$35.83	$35.85	$35.80
Purchase #3	$168.66	11.191%	$187.5347	$187.53	$187.55	$187.50
Purchase #4	$216.30	9.580%	$237.0215	$237.02	$237.00	$237.00
Purchase #5	$45.96	13.171%	$52.0134	$52.01	$52.00	$52.00
Purchase #6	$222.84	12.538%	$250.7797	$250.78	$250.80	$250.80
Purchase #7	$179.90	10.511%	$198.8093	$198.81	$198.80	$198.80
7 purchase totals =	$1,024.16		$1,131.7847	$1,131.78	$1,131.80	$1,131.70