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	$144.82	5.869%	$153.3195	$153.32	$153.30	$153.30
Purchase #2	$47.48	10.860%	$52.6363	$52.64	$52.65	$52.60
Purchase #3	$248.41	7.844%	$267.8953	$267.90	$267.90	$267.90
Purchase #4	$18.93	7.251%	$20.3026	$20.30	$20.30	$20.30
Purchase #5	$55.55	6.288%	$59.043	$59.04	$59.05	$59.00
Purchase #6	$138.75	5.140%	$145.8818	$145.88	$145.90	$145.90
Purchase #7	$95.33	6.811%	$101.8229	$101.82	$101.80	$101.80
7 purchase totals =	$749.27		$800.9014	$800.90	$800.90	$800.80