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	$247.47	13.163%	$280.0445	$280.04	$280.05	$280.00
Purchase #2	$6.61	6.792%	$7.059	$7.06	$7.05	$7.10
Purchase #3	$7.89	12.685%	$8.8908	$8.89	$8.90	$8.90
Purchase #4	$91.50	8.471%	$99.251	$99.25	$99.25	$99.30
Purchase #5	$73.51	5.187%	$77.323	$77.32	$77.30	$77.30
Purchase #6	$128.53	6.488%	$136.869	$136.87	$136.85	$136.90
Purchase #7	$198.88	8.263%	$215.3135	$215.31	$215.30	$215.30
7 purchase totals =	$754.39		$824.7508	$824.74	$824.70	$824.80