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	$125.53	6.674%	$133.9079	$133.91	$133.90	$133.90
Purchase #2	$222.56	10.611%	$246.1758	$246.18	$246.20	$246.20
Purchase #3	$120.50	11.485%	$134.3394	$134.34	$134.35	$134.30
Purchase #4	$134.34	9.765%	$147.4583	$147.46	$147.45	$147.50
Purchase #5	$172.94	13.790%	$196.7884	$196.79	$196.80	$196.80
Purchase #6	$245.89	11.109%	$273.2059	$273.21	$273.20	$273.20
Purchase #7	$140.32	11.667%	$156.6911	$156.69	$156.70	$156.70
7 purchase totals =	$1,162.08		$1,288.5668	$1,288.58	$1,288.60	$1,288.60