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	$25.53	8.629%	$27.733	$27.73	$27.75	$27.70
Purchase #2	$179.96	5.152%	$189.2315	$189.23	$189.25	$189.20
Purchase #3	$18.39	12.213%	$20.636	$20.64	$20.65	$20.60
Purchase #4	$90.58	9.684%	$99.3518	$99.35	$99.35	$99.40
Purchase #5	$68.55	5.815%	$72.5362	$72.54	$72.55	$72.50
Purchase #6	$200.48	7.704%	$215.925	$215.93	$215.95	$215.90
Purchase #7	$67.97	6.849%	$72.6253	$72.63	$72.65	$72.60
7 purchase totals =	$651.46		$698.0388	$698.05	$698.15	$697.90