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	$48.56	7.349%	$52.1287	$52.13	$52.15	$52.10
Purchase #2	$100.76	9.754%	$110.5881	$110.59	$110.60	$110.60
Purchase #3	$98.51	11.546%	$109.884	$109.88	$109.90	$109.90
Purchase #4	$28.45	3.268%	$29.3797	$29.38	$29.40	$29.40
Purchase #5	$63.38	13.126%	$71.6993	$71.70	$71.70	$71.70
Purchase #6	$93.62	6.744%	$99.9337	$99.93	$99.95	$99.90
Purchase #7	$22.50	9.290%	$24.5903	$24.59	$24.60	$24.60
7 purchase totals =	$455.78		$498.2038	$498.20	$498.30	$498.20