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	$83.58	10.163%	$92.0742	$92.07	$92.05	$92.10
Purchase #2	$233.27	5.663%	$246.4801	$246.48	$246.50	$246.50
Purchase #3	$207.41	5.705%	$219.2427	$219.24	$219.25	$219.20
Purchase #4	$6.53	8.345%	$7.0749	$7.07	$7.05	$7.10
Purchase #5	$72.86	8.196%	$78.8316	$78.83	$78.85	$78.80
Purchase #6	$144.35	4.807%	$151.2889	$151.29	$151.30	$151.30
Purchase #7	$23.57	7.270%	$25.2835	$25.28	$25.30	$25.30
7 purchase totals =	$771.57		$820.2759	$820.26	$820.30	$820.30