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	$85.35	6.403%	$90.815	$90.82	$90.80	$90.80
Purchase #2	$163.65	11.415%	$182.3306	$182.33	$182.35	$182.30
Purchase #3	$64.77	10.802%	$71.7665	$71.77	$71.75	$71.80
Purchase #4	$179.44	11.515%	$200.1025	$200.10	$200.10	$200.10
Purchase #5	$233.34	13.844%	$265.6436	$265.64	$265.65	$265.60
Purchase #6	$124.85	5.365%	$131.5482	$131.55	$131.55	$131.50
Purchase #7	$25.33	10.289%	$27.9362	$27.94	$27.95	$27.90
7 purchase totals =	$876.73		$970.1426	$970.15	$970.15	$970.00