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	$81.89	9.179%	$89.4067	$89.41	$89.40	$89.40
Purchase #2	$53.78	8.601%	$58.4056	$58.41	$58.40	$58.40
Purchase #3	$63.82	11.596%	$71.2206	$71.22	$71.20	$71.20
Purchase #4	$69.53	6.324%	$73.9271	$73.93	$73.95	$73.90
Purchase #5	$78.82	5.227%	$82.9399	$82.94	$82.95	$82.90
Purchase #6	$95.96	13.736%	$109.1411	$109.14	$109.15	$109.10
Purchase #7	$35.71	7.422%	$38.3604	$38.36	$38.35	$38.40
7 purchase totals =	$479.51		$523.4014	$523.41	$523.40	$523.30