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	$50.99	4.622%	$53.3468	$53.35	$53.35	$53.30
Purchase #2	$155.35	3.204%	$160.3274	$160.33	$160.35	$160.30
Purchase #3	$69.59	12.412%	$78.2275	$78.23	$78.25	$78.20
Purchase #4	$190.62	3.111%	$196.5502	$196.55	$196.55	$196.60
Purchase #5	$28.86	12.637%	$32.507	$32.51	$32.50	$32.50
Purchase #6	$37.77	11.493%	$42.1109	$42.11	$42.10	$42.10
Purchase #7	$36.37	10.308%	$40.119	$40.12	$40.10	$40.10
7 purchase totals =	$569.55		$603.1888	$603.20	$603.20	$603.10