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	$246.70	3.164%	$254.5056	$254.51	$254.50	$254.50
Purchase #2	$94.47	5.298%	$99.475	$99.48	$99.50	$99.50
Purchase #3	$138.67	5.465%	$146.2483	$146.25	$146.25	$146.20
Purchase #4	$19.77	13.626%	$22.4639	$22.46	$22.45	$22.50
Purchase #5	$163.64	12.635%	$184.3159	$184.32	$184.30	$184.30
Purchase #6	$91.53	5.203%	$96.2923	$96.29	$96.30	$96.30
Purchase #7	$32.63	10.200%	$35.9583	$35.96	$35.95	$36.00
7 purchase totals =	$787.41		$839.2593	$839.27	$839.25	$839.30