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	$81.78	9.290%	$89.3774	$89.38	$89.40	$89.40
Purchase #2	$79.93	9.560%	$87.5713	$87.57	$87.55	$87.60
Purchase #3	$209.90	7.271%	$225.1618	$225.16	$225.15	$225.20
Purchase #4	$194.89	9.490%	$213.3851	$213.39	$213.40	$213.40
Purchase #5	$246.35	7.390%	$264.5553	$264.56	$264.55	$264.60
Purchase #6	$41.96	10.718%	$46.4573	$46.46	$46.45	$46.50
Purchase #7	$216.74	9.584%	$237.5124	$237.51	$237.50	$237.50
7 purchase totals =	$1,071.55		$1,164.0206	$1,164.03	$1,164.00	$1,164.20