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	$249.79	4.709%	$261.5526	$261.55	$261.55	$261.60
Purchase #2	$93.37	9.670%	$102.3989	$102.40	$102.40	$102.40
Purchase #3	$30.50	6.432%	$32.4618	$32.46	$32.45	$32.50
Purchase #4	$65.36	11.368%	$72.7901	$72.79	$72.80	$72.80
Purchase #5	$79.48	11.125%	$88.3222	$88.32	$88.30	$88.30
Purchase #6	$228.36	6.776%	$243.8337	$243.83	$243.85	$243.80
Purchase #7	$106.55	4.350%	$111.1849	$111.18	$111.20	$111.20
7 purchase totals =	$853.41		$912.5442	$912.53	$912.55	$912.60