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	$121.47	4.676%	$127.1499	$127.15	$127.15	$127.10
Purchase #2	$181.43	8.625%	$197.0783	$197.08	$197.10	$197.10
Purchase #3	$249.84	10.817%	$276.8652	$276.87	$276.85	$276.90
Purchase #4	$144.97	13.224%	$164.1408	$164.14	$164.15	$164.10
Purchase #5	$13.50	6.410%	$14.3654	$14.37	$14.35	$14.40
Purchase #6	$57.71	11.113%	$64.1233	$64.12	$64.10	$64.10
Purchase #7	$56.81	4.302%	$59.254	$59.25	$59.25	$59.30
7 purchase totals =	$825.73		$902.9769	$902.98	$902.95	$903.00