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	$172.89	4.273%	$180.2776	$180.28	$180.30	$180.30
Purchase #2	$150.98	9.459%	$165.2612	$165.26	$165.25	$165.30
Purchase #3	$81.49	13.581%	$92.5572	$92.56	$92.55	$92.60
Purchase #4	$45.55	9.488%	$49.8718	$49.87	$49.85	$49.90
Purchase #5	$218.61	8.364%	$236.8945	$236.89	$236.90	$236.90
Purchase #6	$245.50	12.173%	$275.3847	$275.38	$275.40	$275.40
Purchase #7	$58.30	11.718%	$65.1316	$65.13	$65.15	$65.10
7 purchase totals =	$973.32		$1,065.3786	$1,065.37	$1,065.40	$1,065.50