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	$250.61	9.765%	$275.0821	$275.08	$275.10	$275.10
Purchase #2	$59.75	7.242%	$64.0771	$64.08	$64.10	$64.10
Purchase #3	$15.34	3.809%	$15.9243	$15.92	$15.90	$15.90
Purchase #4	$182.86	7.676%	$196.8963	$196.90	$196.90	$196.90
Purchase #5	$86.64	7.798%	$93.3962	$93.40	$93.40	$93.40
Purchase #6	$82.57	11.510%	$92.0738	$92.07	$92.05	$92.10
Purchase #7	$82.92	11.707%	$92.6274	$92.63	$92.65	$92.60
7 purchase totals =	$760.69		$830.0772	$830.08	$830.10	$830.10