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	$105.74	13.438%	$119.9493	$119.95	$119.95	$119.90
Purchase #2	$33.82	10.639%	$37.4181	$37.42	$37.40	$37.40
Purchase #3	$164.27	12.872%	$185.4148	$185.41	$185.40	$185.40
Purchase #4	$80.42	10.769%	$89.0804	$89.08	$89.10	$89.10
Purchase #5	$106.88	3.572%	$110.6978	$110.70	$110.70	$110.70
Purchase #6	$128.56	10.318%	$141.8248	$141.82	$141.80	$141.80
Purchase #7	$105.46	3.334%	$108.976	$108.98	$109.00	$109.00
7 purchase totals =	$725.15		$793.3612	$793.36	$793.35	$793.30