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	$53.64	10.830%	$59.4492	$59.45	$59.45	$59.40
Purchase #2	$116.54	5.763%	$123.2562	$123.26	$123.25	$123.30
Purchase #3	$62.90	13.242%	$71.2292	$71.23	$71.25	$71.20
Purchase #4	$113.27	4.825%	$118.7353	$118.74	$118.75	$118.70
Purchase #5	$83.56	8.736%	$90.8598	$90.86	$90.85	$90.90
Purchase #6	$143.63	12.192%	$161.1414	$161.14	$161.15	$161.10
Purchase #7	$33.26	6.274%	$35.3467	$35.35	$35.35	$35.30
7 purchase totals =	$606.80		$660.0178	$660.03	$660.05	$659.90