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	$99.75	3.318%	$103.0597	$103.06	$103.05	$103.10
Purchase #2	$231.84	5.295%	$244.1159	$244.12	$244.10	$244.10
Purchase #3	$119.63	9.665%	$131.1922	$131.19	$131.20	$131.20
Purchase #4	$86.77	8.850%	$94.4491	$94.45	$94.45	$94.40
Purchase #5	$61.93	9.221%	$67.6406	$67.64	$67.65	$67.60
Purchase #6	$79.83	3.154%	$82.3478	$82.35	$82.35	$82.30
Purchase #7	$168.80	11.571%	$188.3318	$188.33	$188.35	$188.30
7 purchase totals =	$848.55		$911.1371	$911.14	$911.15	$911.00