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	$100.26	9.443%	$109.7276	$109.73	$109.75	$109.70
Purchase #2	$250.47	6.336%	$266.3398	$266.34	$266.35	$266.30
Purchase #3	$93.90	5.766%	$99.3143	$99.31	$99.30	$99.30
Purchase #4	$51.37	5.743%	$54.3202	$54.32	$54.30	$54.30
Purchase #5	$56.80	11.376%	$63.2616	$63.26	$63.25	$63.30
Purchase #6	$233.90	10.314%	$258.0244	$258.02	$258.00	$258.00
Purchase #7	$51.50	4.253%	$53.6903	$53.69	$53.70	$53.70
7 purchase totals =	$838.20		$904.6782	$904.67	$904.65	$904.60