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	$129.70	12.114%	$145.4119	$145.41	$145.40	$145.40
Purchase #2	$38.67	13.198%	$43.7737	$43.77	$43.75	$43.80
Purchase #3	$120.33	9.124%	$131.3089	$131.31	$131.30	$131.30
Purchase #4	$17.47	13.521%	$19.8321	$19.83	$19.85	$19.80
Purchase #5	$133.54	6.421%	$142.1146	$142.11	$142.10	$142.10
Purchase #6	$139.67	4.183%	$145.5124	$145.51	$145.50	$145.50
Purchase #7	$213.90	7.468%	$229.8741	$229.87	$229.85	$229.90
7 purchase totals =	$793.28		$857.8277	$857.81	$857.75	$857.80