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	$89.46	11.842%	$100.0539	$100.05	$100.05	$100.10
Purchase #2	$40.54	4.223%	$42.252	$42.25	$42.25	$42.30
Purchase #3	$203.73	10.160%	$224.429	$224.43	$224.45	$224.40
Purchase #4	$37.63	4.402%	$39.2865	$39.29	$39.30	$39.30
Purchase #5	$121.68	4.774%	$127.489	$127.49	$127.50	$127.50
Purchase #6	$138.91	12.542%	$156.3321	$156.33	$156.35	$156.30
Purchase #7	$54.37	3.630%	$56.3436	$56.34	$56.35	$56.30
7 purchase totals =	$686.32		$746.1861	$746.18	$746.25	$746.20