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	$171.36	3.262%	$176.9498	$176.95	$176.95	$176.90
Purchase #2	$75.28	9.570%	$82.4843	$82.48	$82.50	$82.50
Purchase #3	$37.71	7.736%	$40.6272	$40.63	$40.65	$40.60
Purchase #4	$243.68	9.285%	$266.3057	$266.31	$266.30	$266.30
Purchase #5	$97.26	12.614%	$109.5284	$109.53	$109.55	$109.50
Purchase #6	$153.30	11.157%	$170.4037	$170.40	$170.40	$170.40
Purchase #7	$51.71	6.134%	$54.8819	$54.88	$54.90	$54.90
7 purchase totals =	$830.30		$901.1810	$901.18	$901.25	$901.10