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	$96.90	3.275%	$100.0735	$100.07	$100.05	$100.10
Purchase #2	$210.82	3.822%	$218.8775	$218.88	$218.90	$218.90
Purchase #3	$78.46	12.517%	$88.2808	$88.28	$88.30	$88.30
Purchase #4	$54.81	5.752%	$57.9627	$57.96	$57.95	$58.00
Purchase #5	$17.74	10.132%	$19.5374	$19.54	$19.55	$19.50
Purchase #6	$124.62	5.201%	$131.1015	$131.10	$131.10	$131.10
Purchase #7	$91.41	7.261%	$98.0473	$98.05	$98.05	$98.00
7 purchase totals =	$674.76		$713.8807	$713.88	$713.90	$713.90