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	$166.84	11.684%	$186.3336	$186.33	$186.35	$186.30
Purchase #2	$202.44	5.453%	$213.4791	$213.48	$213.50	$213.50
Purchase #3	$81.59	9.243%	$89.1314	$89.13	$89.15	$89.10
Purchase #4	$178.64	4.295%	$186.3126	$186.31	$186.30	$186.30
Purchase #5	$245.98	4.173%	$256.2447	$256.24	$256.25	$256.20
Purchase #6	$116.87	12.500%	$131.4788	$131.48	$131.50	$131.50
Purchase #7	$42.27	9.642%	$46.3457	$46.35	$46.35	$46.30
7 purchase totals =	$1,034.63		$1,109.3259	$1,109.32	$1,109.40	$1,109.20