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	$51.72	6.622%	$55.1449	$55.14	$55.15	$55.10
Purchase #2	$175.41	9.394%	$191.888	$191.89	$191.90	$191.90
Purchase #3	$232.57	9.468%	$254.5897	$254.59	$254.60	$254.60
Purchase #4	$143.36	5.854%	$151.7523	$151.75	$151.75	$151.80
Purchase #5	$26.76	3.860%	$27.7929	$27.79	$27.80	$27.80
Purchase #6	$206.37	8.812%	$224.5553	$224.56	$224.55	$224.60
Purchase #7	$229.64	8.689%	$249.5934	$249.59	$249.60	$249.60
7 purchase totals =	$1,065.83		$1,155.3165	$1,155.31	$1,155.35	$1,155.40