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	$170.50	10.428%	$188.2797	$188.28	$188.30	$188.30
Purchase #2	$197.47	6.132%	$209.5789	$209.58	$209.60	$209.60
Purchase #3	$232.52	13.831%	$264.6798	$264.68	$264.70	$264.70
Purchase #4	$31.90	5.533%	$33.665	$33.67	$33.65	$33.70
Purchase #5	$181.38	8.453%	$196.7121	$196.71	$196.70	$196.70
Purchase #6	$78.34	9.607%	$85.8661	$85.87	$85.85	$85.90
Purchase #7	$85.54	9.711%	$93.8468	$93.85	$93.85	$93.80
7 purchase totals =	$977.65		$1,072.6284	$1,072.64	$1,072.65	$1,072.70