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	$83.92	8.298%	$90.8837	$90.88	$90.90	$90.90
Purchase #2	$171.37	4.292%	$178.7252	$178.73	$178.75	$178.70
Purchase #3	$55.76	6.257%	$59.2489	$59.25	$59.25	$59.20
Purchase #4	$7.28	7.458%	$7.8229	$7.82	$7.80	$7.80
Purchase #5	$162.39	9.852%	$178.3887	$178.39	$178.40	$178.40
Purchase #6	$100.37	4.336%	$104.722	$104.72	$104.70	$104.70
Purchase #7	$247.29	9.525%	$270.8444	$270.84	$270.85	$270.80
7 purchase totals =	$828.38		$890.6358	$890.63	$890.65	$890.50