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	$76.27	3.597%	$79.0134	$79.01	$79.00	$79.00
Purchase #2	$70.55	11.606%	$78.738	$78.74	$78.75	$78.70
Purchase #3	$43.88	3.644%	$45.479	$45.48	$45.50	$45.50
Purchase #4	$125.88	6.832%	$134.4801	$134.48	$134.50	$134.50
Purchase #5	$75.67	13.710%	$86.0444	$86.04	$86.05	$86.00
Purchase #6	$90.82	4.514%	$94.9196	$94.92	$94.90	$94.90
Purchase #7	$144.90	5.630%	$153.0579	$153.06	$153.05	$153.10
7 purchase totals =	$627.97		$671.7324	$671.73	$671.75	$671.70