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	$227.43	12.855%	$256.6661	$256.67	$256.65	$256.70
Purchase #2	$240.62	9.867%	$264.362	$264.36	$264.35	$264.40
Purchase #3	$173.27	7.535%	$186.3259	$186.33	$186.35	$186.30
Purchase #4	$223.62	4.587%	$233.8774	$233.88	$233.90	$233.90
Purchase #5	$48.97	12.353%	$55.0193	$55.02	$55.00	$55.00
Purchase #6	$57.33	13.222%	$64.9102	$64.91	$64.90	$64.90
Purchase #7	$131.71	5.585%	$139.066	$139.07	$139.05	$139.10
7 purchase totals =	$1,102.95		$1,200.2269	$1,200.24	$1,200.20	$1,200.30