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	$81.42	8.836%	$88.6143	$88.61	$88.60	$88.60
Purchase #2	$126.62	9.591%	$138.7641	$138.76	$138.75	$138.80
Purchase #3	$188.67	4.121%	$196.4451	$196.45	$196.45	$196.40
Purchase #4	$83.53	10.812%	$92.5613	$92.56	$92.55	$92.60
Purchase #5	$224.45	9.236%	$245.1802	$245.18	$245.20	$245.20
Purchase #6	$120.81	6.601%	$128.7847	$128.78	$128.80	$128.80
Purchase #7	$194.91	4.428%	$203.5406	$203.54	$203.55	$203.50
7 purchase totals =	$1,020.41		$1,093.8903	$1,093.88	$1,093.90	$1,093.90