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	$89.82	3.578%	$93.0338	$93.03	$93.05	$93.00
Purchase #2	$140.90	7.747%	$151.8155	$151.82	$151.80	$151.80
Purchase #3	$70.41	6.616%	$75.0683	$75.07	$75.05	$75.10
Purchase #4	$65.79	10.691%	$72.8236	$72.82	$72.80	$72.80
Purchase #5	$33.32	7.479%	$35.812	$35.81	$35.80	$35.80
Purchase #6	$173.57	3.506%	$179.6554	$179.66	$179.65	$179.70
Purchase #7	$203.45	9.276%	$222.322	$222.32	$222.30	$222.30
7 purchase totals =	$777.26		$830.5306	$830.53	$830.45	$830.50