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	$115.82	12.394%	$130.1747	$130.17	$130.15	$130.20
Purchase #2	$171.98	4.836%	$180.297	$180.30	$180.30	$180.30
Purchase #3	$159.97	12.834%	$180.5005	$180.50	$180.50	$180.50
Purchase #4	$96.57	3.866%	$100.3034	$100.30	$100.30	$100.30
Purchase #5	$79.71	5.106%	$83.78	$83.78	$83.80	$83.80
Purchase #6	$194.47	7.279%	$208.6255	$208.63	$208.65	$208.60
Purchase #7	$30.94	13.790%	$35.2066	$35.21	$35.20	$35.20
7 purchase totals =	$849.46		$918.8877	$918.89	$918.90	$918.90