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	$186.29	12.478%	$209.5353	$209.54	$209.55	$209.50
Purchase #2	$73.55	12.739%	$82.9195	$82.92	$82.90	$82.90
Purchase #3	$74.96	10.749%	$83.0175	$83.02	$83.00	$83.00
Purchase #4	$50.75	10.543%	$56.1006	$56.10	$56.10	$56.10
Purchase #5	$33.40	10.719%	$36.9801	$36.98	$37.00	$37.00
Purchase #6	$27.83	12.672%	$31.3566	$31.36	$31.35	$31.40
Purchase #7	$156.45	8.304%	$169.4416	$169.44	$169.45	$169.40
7 purchase totals =	$603.23		$669.3512	$669.36	$669.35	$669.30