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	$124.75	11.700%	$139.3458	$139.35	$139.35	$139.30
Purchase #2	$115.90	8.140%	$125.3343	$125.33	$125.35	$125.30
Purchase #3	$231.99	9.298%	$253.5604	$253.56	$253.55	$253.60
Purchase #4	$57.53	6.749%	$61.4127	$61.41	$61.40	$61.40
Purchase #5	$47.30	13.247%	$53.5658	$53.57	$53.55	$53.60
Purchase #6	$170.86	9.756%	$187.5291	$187.53	$187.55	$187.50
Purchase #7	$142.31	7.217%	$152.5805	$152.58	$152.60	$152.60
7 purchase totals =	$890.64		$973.3286	$973.33	$973.35	$973.30