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	$246.84	13.535%	$280.2498	$280.25	$280.25	$280.20
Purchase #2	$95.36	4.130%	$99.2984	$99.30	$99.30	$99.30
Purchase #3	$41.85	6.281%	$44.4786	$44.48	$44.50	$44.50
Purchase #4	$145.84	9.315%	$159.425	$159.43	$159.45	$159.40
Purchase #5	$25.59	11.153%	$28.4441	$28.44	$28.45	$28.40
Purchase #6	$101.31	11.806%	$113.2707	$113.27	$113.25	$113.30
Purchase #7	$48.27	12.518%	$54.3124	$54.31	$54.30	$54.30
7 purchase totals =	$705.06		$779.4790	$779.48	$779.50	$779.40