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	$142.72	6.624%	$152.1738	$152.17	$152.15	$152.20
Purchase #2	$18.49	13.673%	$21.0181	$21.02	$21.00	$21.00
Purchase #3	$57.81	6.216%	$61.4035	$61.40	$61.40	$61.40
Purchase #4	$235.34	13.807%	$267.8334	$267.83	$267.85	$267.80
Purchase #5	$51.89	6.520%	$55.2732	$55.27	$55.25	$55.30
Purchase #6	$173.78	3.775%	$180.3402	$180.34	$180.35	$180.30
Purchase #7	$72.54	4.600%	$75.8768	$75.88	$75.90	$75.90
7 purchase totals =	$752.57		$813.9190	$813.91	$813.90	$813.90