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	$147.90	11.820%	$165.3818	$165.38	$165.40	$165.40
Purchase #2	$210.66	6.299%	$223.9295	$223.93	$223.95	$223.90
Purchase #3	$134.79	13.163%	$152.5324	$152.53	$152.55	$152.50
Purchase #4	$96.40	3.131%	$99.4183	$99.42	$99.40	$99.40
Purchase #5	$216.47	10.819%	$239.8899	$239.89	$239.90	$239.90
Purchase #6	$20.33	6.713%	$21.6948	$21.69	$21.70	$21.70
Purchase #7	$232.66	12.669%	$262.1357	$262.14	$262.15	$262.10
7 purchase totals =	$1,059.21		$1,164.9824	$1,164.98	$1,165.05	$1,164.90