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	$179.59	6.600%	$191.4429	$191.44	$191.45	$191.40
Purchase #2	$126.98	10.835%	$140.7383	$140.74	$140.75	$140.70
Purchase #3	$63.82	3.623%	$66.1322	$66.13	$66.15	$66.10
Purchase #4	$116.33	9.611%	$127.5105	$127.51	$127.50	$127.50
Purchase #5	$215.72	9.802%	$236.8649	$236.86	$236.85	$236.90
Purchase #6	$102.43	8.122%	$110.7494	$110.75	$110.75	$110.70
Purchase #7	$88.55	12.156%	$99.3141	$99.31	$99.30	$99.30
7 purchase totals =	$893.42		$972.7523	$972.74	$972.75	$972.60