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	$28.50	10.462%	$31.4817	$31.48	$31.50	$31.50
Purchase #2	$160.95	10.169%	$177.317	$177.32	$177.30	$177.30
Purchase #3	$197.28	6.610%	$210.3202	$210.32	$210.30	$210.30
Purchase #4	$7.61	7.418%	$8.1745	$8.17	$8.15	$8.20
Purchase #5	$169.77	9.492%	$185.8846	$185.88	$185.90	$185.90
Purchase #6	$47.89	6.722%	$51.1092	$51.11	$51.10	$51.10
Purchase #7	$27.35	5.669%	$28.9005	$28.90	$28.90	$28.90
7 purchase totals =	$639.35		$693.1877	$693.18	$693.15	$693.20