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	$128.38	10.552%	$141.9267	$141.93	$141.95	$141.90
Purchase #2	$59.93	7.135%	$64.206	$64.21	$64.20	$64.20
Purchase #3	$56.64	6.470%	$60.3046	$60.30	$60.30	$60.30
Purchase #4	$67.52	6.359%	$71.8136	$71.81	$71.80	$71.80
Purchase #5	$115.96	6.747%	$123.7838	$123.78	$123.80	$123.80
Purchase #6	$56.31	3.830%	$58.4667	$58.47	$58.45	$58.50
Purchase #7	$33.57	6.566%	$35.7742	$35.77	$35.75	$35.80
7 purchase totals =	$518.31		$556.2756	$556.27	$556.25	$556.30