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	$206.88	6.228%	$219.7645	$219.76	$219.75	$219.80
Purchase #2	$21.90	10.361%	$24.1691	$24.17	$24.15	$24.20
Purchase #3	$98.88	10.585%	$109.3464	$109.35	$109.35	$109.30
Purchase #4	$222.53	12.756%	$250.9159	$250.92	$250.90	$250.90
Purchase #5	$80.31	13.698%	$91.3109	$91.31	$91.30	$91.30
Purchase #6	$182.98	9.796%	$200.9047	$200.90	$200.90	$200.90
Purchase #7	$100.88	9.827%	$110.7935	$110.79	$110.80	$110.80
7 purchase totals =	$914.36		$1,007.2050	$1,007.20	$1,007.15	$1,007.20