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	$200.27	12.233%	$224.769	$224.77	$224.75	$224.80
Purchase #2	$172.97	5.538%	$182.5491	$182.55	$182.55	$182.50
Purchase #3	$20.44	7.266%	$21.9252	$21.93	$21.95	$21.90
Purchase #4	$245.41	4.704%	$256.9541	$256.95	$256.95	$257.00
Purchase #5	$151.41	9.174%	$165.3004	$165.30	$165.30	$165.30
Purchase #6	$59.57	11.310%	$66.3074	$66.31	$66.30	$66.30
Purchase #7	$82.72	10.607%	$91.4941	$91.49	$91.50	$91.50
7 purchase totals =	$932.79		$1,009.2993	$1,009.30	$1,009.30	$1,009.30