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	$242.78	3.519%	$251.3234	$251.32	$251.30	$251.30
Purchase #2	$82.37	11.506%	$91.8475	$91.85	$91.85	$91.80
Purchase #3	$250.71	10.691%	$277.5134	$277.51	$277.50	$277.50
Purchase #4	$68.54	11.672%	$76.54	$76.54	$76.55	$76.50
Purchase #5	$88.52	11.394%	$98.606	$98.61	$98.60	$98.60
Purchase #6	$86.32	5.400%	$90.9813	$90.98	$91.00	$91.00
Purchase #7	$73.96	5.823%	$78.2667	$78.27	$78.25	$78.30
7 purchase totals =	$893.20		$965.0783	$965.08	$965.05	$965.00