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	$36.73	3.208%	$37.9083	$37.91	$37.90	$37.90
Purchase #2	$42.33	10.746%	$46.8788	$46.88	$46.90	$46.90
Purchase #3	$84.30	7.728%	$90.8147	$90.81	$90.80	$90.80
Purchase #4	$173.64	12.623%	$195.5586	$195.56	$195.55	$195.60
Purchase #5	$64.64	10.342%	$71.3251	$71.33	$71.35	$71.30
Purchase #6	$5.51	12.797%	$6.2151	$6.22	$6.20	$6.20
Purchase #7	$55.43	9.820%	$60.8732	$60.87	$60.85	$60.90
7 purchase totals =	$462.58		$509.5738	$509.58	$509.55	$509.60