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	$229.40	9.181%	$250.4612	$250.46	$250.45	$250.50
Purchase #2	$178.25	13.582%	$202.4599	$202.46	$202.45	$202.50
Purchase #3	$200.49	4.459%	$209.4298	$209.43	$209.45	$209.40
Purchase #4	$72.62	10.755%	$80.4303	$80.43	$80.45	$80.40
Purchase #5	$232.38	11.596%	$259.3268	$259.33	$259.35	$259.30
Purchase #6	$24.89	11.645%	$27.7884	$27.79	$27.80	$27.80
Purchase #7	$56.85	8.365%	$61.6055	$61.61	$61.60	$61.60
7 purchase totals =	$994.88		$1,091.5019	$1,091.51	$1,091.55	$1,091.50