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	$84.88	3.848%	$88.1462	$88.15	$88.15	$88.10
Purchase #2	$105.38	3.853%	$109.4403	$109.44	$109.45	$109.40
Purchase #3	$236.97	3.663%	$245.6502	$245.65	$245.65	$245.70
Purchase #4	$52.81	3.179%	$54.4888	$54.49	$54.50	$54.50
Purchase #5	$209.80	5.411%	$221.1523	$221.15	$221.15	$221.20
Purchase #6	$38.85	8.406%	$42.1157	$42.12	$42.10	$42.10
Purchase #7	$125.77	10.770%	$139.3154	$139.32	$139.30	$139.30
7 purchase totals =	$854.46		$900.3089	$900.32	$900.30	$900.30