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	$48.61	5.502%	$51.2845	$51.28	$51.30	$51.30
Purchase #2	$78.75	4.581%	$82.3575	$82.36	$82.35	$82.40
Purchase #3	$100.76	8.474%	$109.2984	$109.30	$109.30	$109.30
Purchase #4	$166.64	11.617%	$185.9986	$186.00	$186.00	$186.00
Purchase #5	$204.65	8.559%	$222.166	$222.17	$222.15	$222.20
Purchase #6	$244.61	10.421%	$270.1008	$270.10	$270.10	$270.10
Purchase #7	$250.60	7.249%	$268.766	$268.77	$268.75	$268.80
7 purchase totals =	$1,094.62		$1,189.9718	$1,189.98	$1,189.95	$1,190.10