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	$159.69	13.271%	$180.8825	$180.88	$180.90	$180.90
Purchase #2	$64.69	4.859%	$67.8333	$67.83	$67.85	$67.80
Purchase #3	$243.72	4.603%	$254.9384	$254.94	$254.95	$254.90
Purchase #4	$7.56	5.588%	$7.9825	$7.98	$8.00	$8.00
Purchase #5	$196.80	3.857%	$204.3906	$204.39	$204.40	$204.40
Purchase #6	$95.63	6.112%	$101.4749	$101.47	$101.45	$101.50
Purchase #7	$85.76	11.847%	$95.92	$95.92	$95.90	$95.90
7 purchase totals =	$853.85		$913.4222	$913.41	$913.45	$913.40