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	$181.34	13.295%	$205.4492	$205.45	$205.45	$205.40
Purchase #2	$200.37	4.717%	$209.8215	$209.82	$209.80	$209.80
Purchase #3	$82.55	10.263%	$91.0221	$91.02	$91.00	$91.00
Purchase #4	$27.50	13.338%	$31.168	$31.17	$31.15	$31.20
Purchase #5	$176.37	4.199%	$183.7758	$183.78	$183.80	$183.80
Purchase #6	$6.85	5.124%	$7.201	$7.20	$7.20	$7.20
Purchase #7	$221.35	13.186%	$250.5372	$250.54	$250.55	$250.50
7 purchase totals =	$896.33		$978.9748	$978.98	$978.95	$978.90