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	$175.98	12.109%	$197.2894	$197.29	$197.30	$197.30
Purchase #2	$236.57	13.657%	$268.8784	$268.88	$268.90	$268.90
Purchase #3	$171.64	8.872%	$186.8679	$186.87	$186.85	$186.90
Purchase #4	$148.59	11.165%	$165.1801	$165.18	$165.20	$165.20
Purchase #5	$80.42	6.368%	$85.5411	$85.54	$85.55	$85.50
Purchase #6	$17.47	6.373%	$18.5834	$18.58	$18.60	$18.60
Purchase #7	$54.88	7.776%	$59.1475	$59.15	$59.15	$59.10
7 purchase totals =	$885.55		$981.4878	$981.49	$981.55	$981.50