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	$171.99	7.874%	$185.5325	$185.53	$185.55	$185.50
Purchase #2	$162.62	11.498%	$181.318	$181.32	$181.30	$181.30
Purchase #3	$119.57	6.546%	$127.3971	$127.40	$127.40	$127.40
Purchase #4	$217.65	13.327%	$246.6562	$246.66	$246.65	$246.70
Purchase #5	$27.36	11.646%	$30.5463	$30.55	$30.55	$30.50
Purchase #6	$50.58	13.185%	$57.249	$57.25	$57.25	$57.20
Purchase #7	$18.82	11.122%	$20.9132	$20.91	$20.90	$20.90
7 purchase totals =	$768.59		$849.6123	$849.62	$849.60	$849.50