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	$91.30	12.655%	$102.854	$102.85	$102.85	$102.90
Purchase #2	$86.69	3.174%	$89.4415	$89.44	$89.45	$89.40
Purchase #3	$17.93	13.210%	$20.2986	$20.30	$20.30	$20.30
Purchase #4	$72.38	11.611%	$80.784	$80.78	$80.80	$80.80
Purchase #5	$54.73	9.588%	$59.9775	$59.98	$60.00	$60.00
Purchase #6	$147.91	7.854%	$159.5269	$159.53	$159.55	$159.50
Purchase #7	$80.71	12.425%	$90.7382	$90.74	$90.75	$90.70
7 purchase totals =	$551.65		$603.6207	$603.62	$603.70	$603.60