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	$76.88	12.803%	$86.7229	$86.72	$86.70	$86.70
Purchase #2	$38.59	7.216%	$41.3747	$41.37	$41.35	$41.40
Purchase #3	$64.25	11.200%	$71.446	$71.45	$71.45	$71.40
Purchase #4	$170.40	7.719%	$183.5532	$183.55	$183.55	$183.60
Purchase #5	$99.85	10.460%	$110.2943	$110.29	$110.30	$110.30
Purchase #6	$162.57	7.140%	$174.1775	$174.18	$174.20	$174.20
Purchase #7	$103.59	5.439%	$109.2243	$109.22	$109.20	$109.20
7 purchase totals =	$716.13		$776.7929	$776.78	$776.75	$776.80