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	$66.66	7.755%	$71.8295	$71.83	$71.85	$71.80
Purchase #2	$25.93	9.740%	$28.4556	$28.46	$28.45	$28.50
Purchase #3	$229.47	12.174%	$257.4057	$257.41	$257.40	$257.40
Purchase #4	$89.81	5.201%	$94.481	$94.48	$94.50	$94.50
Purchase #5	$25.74	5.570%	$27.1737	$27.17	$27.15	$27.20
Purchase #6	$64.52	12.448%	$72.5514	$72.55	$72.55	$72.60
Purchase #7	$249.38	6.590%	$265.8141	$265.81	$265.80	$265.80
7 purchase totals =	$751.51		$817.7110	$817.71	$817.70	$817.80