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	$211.31	10.320%	$233.1172	$233.12	$233.10	$233.10
Purchase #2	$105.67	6.734%	$112.7858	$112.79	$112.80	$112.80
Purchase #3	$98.59	4.587%	$103.1123	$103.11	$103.10	$103.10
Purchase #4	$22.72	12.367%	$25.5298	$25.53	$25.55	$25.50
Purchase #5	$156.89	7.277%	$168.3069	$168.31	$168.30	$168.30
Purchase #6	$91.81	9.540%	$100.5687	$100.57	$100.55	$100.60
Purchase #7	$196.92	8.335%	$213.3333	$213.33	$213.35	$213.30
7 purchase totals =	$883.91		$956.7540	$956.76	$956.75	$956.70