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	$28.98	9.155%	$31.6331	$31.63	$31.65	$31.60
Purchase #2	$123.71	6.268%	$131.4641	$131.46	$131.45	$131.50
Purchase #3	$53.93	13.133%	$61.0126	$61.01	$61.00	$61.00
Purchase #4	$232.26	13.358%	$263.2853	$263.29	$263.30	$263.30
Purchase #5	$107.63	9.350%	$117.6934	$117.69	$117.70	$117.70
Purchase #6	$78.57	9.226%	$85.8189	$85.82	$85.80	$85.80
Purchase #7	$40.98	6.269%	$43.549	$43.55	$43.55	$43.50
7 purchase totals =	$666.06		$734.4564	$734.45	$734.45	$734.40