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	$186.89	10.512%	$206.5359	$206.54	$206.55	$206.50
Purchase #2	$37.48	8.745%	$40.7576	$40.76	$40.75	$40.80
Purchase #3	$58.81	4.681%	$61.5629	$61.56	$61.55	$61.60
Purchase #4	$104.39	5.283%	$109.9049	$109.90	$109.90	$109.90
Purchase #5	$85.35	11.860%	$95.4725	$95.47	$95.45	$95.50
Purchase #6	$21.57	4.401%	$22.5193	$22.52	$22.50	$22.50
Purchase #7	$5.62	10.579%	$6.2145	$6.21	$6.20	$6.20
7 purchase totals =	$500.11		$542.9676	$542.96	$542.90	$543.00