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	$188.84	6.394%	$200.9144	$200.91	$200.90	$200.90
Purchase #2	$158.56	6.468%	$168.8157	$168.82	$168.80	$168.80
Purchase #3	$222.40	12.451%	$250.091	$250.09	$250.10	$250.10
Purchase #4	$246.66	13.524%	$280.0183	$280.02	$280.00	$280.00
Purchase #5	$99.75	5.778%	$105.5136	$105.51	$105.50	$105.50
Purchase #6	$224.30	13.448%	$254.4639	$254.46	$254.45	$254.50
Purchase #7	$213.83	13.643%	$243.0028	$243.00	$243.00	$243.00
7 purchase totals =	$1,354.34		$1,502.8197	$1,502.81	$1,502.75	$1,502.80