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	$31.33	4.194%	$32.644	$32.64	$32.65	$32.60
Purchase #2	$192.40	13.192%	$217.7814	$217.78	$217.80	$217.80
Purchase #3	$154.74	12.809%	$174.5606	$174.56	$174.55	$174.60
Purchase #4	$67.28	8.496%	$72.9961	$73.00	$73.00	$73.00
Purchase #5	$54.66	9.449%	$59.8248	$59.82	$59.80	$59.80
Purchase #6	$61.49	11.609%	$68.6284	$68.63	$68.65	$68.60
Purchase #7	$139.88	11.528%	$156.0054	$156.01	$156.00	$156.00
7 purchase totals =	$701.78		$782.4407	$782.44	$782.45	$782.40