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	$39.92	5.355%	$42.0577	$42.06	$42.05	$42.10
Purchase #2	$249.59	7.348%	$267.9299	$267.93	$267.95	$267.90
Purchase #3	$98.46	4.788%	$103.1743	$103.17	$103.15	$103.20
Purchase #4	$73.60	4.542%	$76.9429	$76.94	$76.95	$76.90
Purchase #5	$216.95	7.426%	$233.0607	$233.06	$233.05	$233.10
Purchase #6	$9.72	8.368%	$10.5334	$10.53	$10.55	$10.50
Purchase #7	$142.63	6.803%	$152.3331	$152.33	$152.35	$152.30
7 purchase totals =	$830.87		$886.0320	$886.02	$886.05	$886.00