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	$123.73	3.699%	$128.3068	$128.31	$128.30	$128.30
Purchase #2	$196.86	12.871%	$222.1979	$222.20	$222.20	$222.20
Purchase #3	$182.52	10.834%	$202.2942	$202.29	$202.30	$202.30
Purchase #4	$237.41	12.299%	$266.6091	$266.61	$266.60	$266.60
Purchase #5	$171.89	11.421%	$191.5216	$191.52	$191.50	$191.50
Purchase #6	$47.96	5.565%	$50.629	$50.63	$50.65	$50.60
Purchase #7	$81.70	5.161%	$85.9165	$85.92	$85.90	$85.90
7 purchase totals =	$1,042.07		$1,147.4751	$1,147.48	$1,147.45	$1,147.40