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	$208.65	6.283%	$221.7595	$221.76	$221.75	$221.80
Purchase #2	$217.25	10.199%	$239.4073	$239.41	$239.40	$239.40
Purchase #3	$53.82	11.280%	$59.8909	$59.89	$59.90	$59.90
Purchase #4	$72.84	10.596%	$80.5581	$80.56	$80.55	$80.60
Purchase #5	$123.63	8.862%	$134.5861	$134.59	$134.60	$134.60
Purchase #6	$67.70	5.224%	$71.2366	$71.24	$71.25	$71.20
Purchase #7	$219.47	6.802%	$234.3983	$234.40	$234.40	$234.40
7 purchase totals =	$963.36		$1,041.8368	$1,041.85	$1,041.85	$1,041.90