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	$23.52	7.322%	$25.2421	$25.24	$25.25	$25.20
Purchase #2	$142.46	9.843%	$156.4823	$156.48	$156.50	$156.50
Purchase #3	$79.42	5.137%	$83.4998	$83.50	$83.50	$83.50
Purchase #4	$12.98	11.739%	$14.5037	$14.50	$14.50	$14.50
Purchase #5	$15.41	9.679%	$16.9015	$16.90	$16.90	$16.90
Purchase #6	$140.84	7.449%	$151.3312	$151.33	$151.35	$151.30
Purchase #7	$42.92	12.809%	$48.4176	$48.42	$48.40	$48.40
7 purchase totals =	$457.55		$496.3782	$496.37	$496.40	$496.30