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	$206.65	12.165%	$231.789	$231.79	$231.80	$231.80
Purchase #2	$216.57	12.825%	$244.3451	$244.35	$244.35	$244.30
Purchase #3	$83.80	11.623%	$93.5401	$93.54	$93.55	$93.50
Purchase #4	$52.85	3.172%	$54.5264	$54.53	$54.55	$54.50
Purchase #5	$246.99	8.294%	$267.4754	$267.48	$267.50	$267.50
Purchase #6	$55.40	7.608%	$59.6148	$59.61	$59.60	$59.60
Purchase #7	$130.89	6.444%	$139.3246	$139.32	$139.30	$139.30
7 purchase totals =	$993.15		$1,090.6154	$1,090.62	$1,090.65	$1,090.50