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	$40.76	3.775%	$42.2987	$42.30	$42.30	$42.30
Purchase #2	$203.43	6.303%	$216.2522	$216.25	$216.25	$216.30
Purchase #3	$110.65	3.457%	$114.4752	$114.48	$114.50	$114.50
Purchase #4	$46.86	10.788%	$51.9153	$51.92	$51.90	$51.90
Purchase #5	$199.91	4.123%	$208.1523	$208.15	$208.15	$208.20
Purchase #6	$45.43	11.148%	$50.4945	$50.49	$50.50	$50.50
Purchase #7	$138.73	8.666%	$150.7523	$150.75	$150.75	$150.80
7 purchase totals =	$785.77		$834.3405	$834.34	$834.35	$834.50