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	$104.85	10.711%	$116.0805	$116.08	$116.10	$116.10
Purchase #2	$59.98	4.336%	$62.5807	$62.58	$62.60	$62.60
Purchase #3	$82.48	11.417%	$91.8967	$91.90	$91.90	$91.90
Purchase #4	$243.43	8.654%	$264.4964	$264.50	$264.50	$264.50
Purchase #5	$134.56	9.784%	$147.7254	$147.73	$147.75	$147.70
Purchase #6	$112.57	6.293%	$119.654	$119.65	$119.65	$119.70
Purchase #7	$111.72	10.405%	$123.3445	$123.34	$123.35	$123.30
7 purchase totals =	$849.59		$925.7782	$925.78	$925.85	$925.80