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	$88.58	12.441%	$99.6002	$99.60	$99.60	$99.60
Purchase #2	$75.59	13.815%	$86.0328	$86.03	$86.05	$86.00
Purchase #3	$164.67	4.253%	$171.6734	$171.67	$171.65	$171.70
Purchase #4	$125.88	11.438%	$140.2782	$140.28	$140.30	$140.30
Purchase #5	$192.55	3.445%	$199.1833	$199.18	$199.20	$199.20
Purchase #6	$197.32	13.336%	$223.6346	$223.63	$223.65	$223.60
Purchase #7	$221.57	11.211%	$246.4102	$246.41	$246.40	$246.40
7 purchase totals =	$1,066.16		$1,166.8127	$1,166.80	$1,166.85	$1,166.80