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	$125.89	9.845%	$138.2839	$138.28	$138.30	$138.30
Purchase #2	$93.34	9.350%	$102.0673	$102.07	$102.05	$102.10
Purchase #3	$123.79	3.529%	$128.1585	$128.16	$128.15	$128.20
Purchase #4	$72.92	7.112%	$78.1061	$78.11	$78.10	$78.10
Purchase #5	$80.38	11.276%	$89.4436	$89.44	$89.45	$89.40
Purchase #6	$68.88	3.440%	$71.2495	$71.25	$71.25	$71.20
Purchase #7	$164.98	10.781%	$182.7665	$182.77	$182.75	$182.80
7 purchase totals =	$730.18		$790.0754	$790.08	$790.05	$790.10