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	$46.90	6.783%	$50.0812	$50.08	$50.10	$50.10
Purchase #2	$141.51	7.639%	$152.3199	$152.32	$152.30	$152.30
Purchase #3	$47.26	13.459%	$53.6207	$53.62	$53.60	$53.60
Purchase #4	$73.95	12.361%	$83.091	$83.09	$83.10	$83.10
Purchase #5	$79.29	9.180%	$86.5688	$86.57	$86.55	$86.60
Purchase #6	$87.91	12.524%	$98.9198	$98.92	$98.90	$98.90
Purchase #7	$57.56	4.712%	$60.2722	$60.27	$60.25	$60.30
7 purchase totals =	$534.38		$584.8736	$584.87	$584.80	$584.90