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	$109.40	7.314%	$117.4015	$117.40	$117.40	$117.40
Purchase #2	$246.74	8.362%	$267.3724	$267.37	$267.35	$267.40
Purchase #3	$240.36	3.424%	$248.5899	$248.59	$248.60	$248.60
Purchase #4	$122.28	7.837%	$131.8631	$131.86	$131.85	$131.90
Purchase #5	$72.85	11.603%	$81.3028	$81.30	$81.30	$81.30
Purchase #6	$50.33	5.776%	$53.2371	$53.24	$53.25	$53.20
Purchase #7	$152.84	12.426%	$171.8319	$171.83	$171.85	$171.80
7 purchase totals =	$994.80		$1,071.5987	$1,071.59	$1,071.60	$1,071.60