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	$89.55	12.650%	$100.8781	$100.88	$100.90	$100.90
Purchase #2	$171.30	8.178%	$185.3089	$185.31	$185.30	$185.30
Purchase #3	$171.77	12.273%	$192.8513	$192.85	$192.85	$192.90
Purchase #4	$69.69	3.650%	$72.2337	$72.23	$72.25	$72.20
Purchase #5	$151.40	9.324%	$165.5165	$165.52	$165.50	$165.50
Purchase #6	$67.67	12.763%	$76.3067	$76.31	$76.30	$76.30
Purchase #7	$103.66	9.799%	$113.8176	$113.82	$113.80	$113.80
7 purchase totals =	$825.04		$906.9128	$906.92	$906.90	$906.90