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	$156.32	7.600%	$168.2003	$168.20	$168.20	$168.20
Purchase #2	$43.60	4.226%	$45.4425	$45.44	$45.45	$45.40
Purchase #3	$100.57	9.598%	$110.2227	$110.22	$110.20	$110.20
Purchase #4	$188.33	3.575%	$195.0628	$195.06	$195.05	$195.10
Purchase #5	$57.68	7.144%	$61.8007	$61.80	$61.80	$61.80
Purchase #6	$123.66	6.520%	$131.7226	$131.72	$131.70	$131.70
Purchase #7	$237.71	9.861%	$261.1506	$261.15	$261.15	$261.20
7 purchase totals =	$907.87		$973.6022	$973.59	$973.55	$973.60