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	$27.85	12.466%	$31.3218	$31.32	$31.30	$31.30
Purchase #2	$42.48	10.391%	$46.8941	$46.89	$46.90	$46.90
Purchase #3	$232.84	5.810%	$246.368	$246.37	$246.35	$246.40
Purchase #4	$152.48	12.576%	$171.6559	$171.66	$171.65	$171.70
Purchase #5	$245.45	9.663%	$269.1678	$269.17	$269.15	$269.20
Purchase #6	$157.65	10.441%	$174.1102	$174.11	$174.10	$174.10
Purchase #7	$158.34	8.612%	$171.9762	$171.98	$172.00	$172.00
7 purchase totals =	$1,017.09		$1,111.4940	$1,111.50	$1,111.45	$1,111.60