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	$38.52	11.223%	$42.8431	$42.84	$42.85	$42.80
Purchase #2	$16.68	9.513%	$18.2668	$18.27	$18.25	$18.30
Purchase #3	$210.27	9.300%	$229.8251	$229.83	$229.85	$229.80
Purchase #4	$72.51	8.749%	$78.8539	$78.85	$78.85	$78.90
Purchase #5	$88.86	10.174%	$97.9006	$97.90	$97.90	$97.90
Purchase #6	$232.26	6.454%	$247.2501	$247.25	$247.25	$247.30
Purchase #7	$170.69	13.531%	$193.7861	$193.79	$193.80	$193.80
7 purchase totals =	$829.79		$908.7257	$908.73	$908.75	$908.80