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	$17.53	5.612%	$18.5138	$18.51	$18.50	$18.50
Purchase #2	$93.89	11.708%	$104.8826	$104.88	$104.90	$104.90
Purchase #3	$178.41	12.221%	$200.2135	$200.21	$200.20	$200.20
Purchase #4	$61.74	4.145%	$64.2991	$64.30	$64.30	$64.30
Purchase #5	$150.26	3.391%	$155.3553	$155.36	$155.35	$155.40
Purchase #6	$64.43	11.578%	$71.8897	$71.89	$71.90	$71.90
Purchase #7	$114.76	12.691%	$129.3242	$129.32	$129.30	$129.30
7 purchase totals =	$681.02		$744.4782	$744.47	$744.45	$744.50