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	$89.57	12.154%	$100.4563	$100.46	$100.45	$100.50
Purchase #2	$59.54	8.354%	$64.514	$64.51	$64.50	$64.50
Purchase #3	$24.93	13.349%	$28.2579	$28.26	$28.25	$28.30
Purchase #4	$142.44	13.470%	$161.6267	$161.63	$161.65	$161.60
Purchase #5	$228.65	9.402%	$250.1477	$250.15	$250.15	$250.10
Purchase #6	$77.51	5.815%	$82.0172	$82.02	$82.00	$82.00
Purchase #7	$6.62	12.252%	$7.4311	$7.43	$7.45	$7.40
7 purchase totals =	$629.26		$694.4509	$694.46	$694.45	$694.40