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	$108.76	13.843%	$123.8156	$123.82	$123.80	$123.80
Purchase #2	$90.55	3.695%	$93.8958	$93.90	$93.90	$93.90
Purchase #3	$235.36	6.621%	$250.9432	$250.94	$250.95	$250.90
Purchase #4	$16.76	10.817%	$18.5729	$18.57	$18.55	$18.60
Purchase #5	$21.64	5.731%	$22.8802	$22.88	$22.90	$22.90
Purchase #6	$21.58	3.279%	$22.2876	$22.29	$22.30	$22.30
Purchase #7	$68.81	13.322%	$77.9769	$77.98	$78.00	$78.00
7 purchase totals =	$563.46		$610.3722	$610.38	$610.40	$610.40