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	$18.87	11.405%	$21.0221	$21.02	$21.00	$21.00
Purchase #2	$141.43	6.187%	$150.1803	$150.18	$150.20	$150.20
Purchase #3	$85.72	6.209%	$91.0424	$91.04	$91.05	$91.00
Purchase #4	$184.54	5.607%	$194.8872	$194.89	$194.90	$194.90
Purchase #5	$132.89	10.630%	$147.0162	$147.02	$147.00	$147.00
Purchase #6	$194.66	10.682%	$215.4536	$215.45	$215.45	$215.50
Purchase #7	$231.33	9.711%	$253.7945	$253.79	$253.80	$253.80
7 purchase totals =	$989.44		$1,073.3963	$1,073.39	$1,073.40	$1,073.40