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	$162.82	3.192%	$168.0172	$168.02	$168.00	$168.00
Purchase #2	$96.85	8.300%	$104.8886	$104.89	$104.90	$104.90
Purchase #3	$94.82	5.543%	$100.0759	$100.08	$100.10	$100.10
Purchase #4	$212.65	4.735%	$222.719	$222.72	$222.70	$222.70
Purchase #5	$134.44	10.158%	$148.0964	$148.10	$148.10	$148.10
Purchase #6	$178.39	4.107%	$185.7165	$185.72	$185.70	$185.70
Purchase #7	$110.54	9.201%	$120.7108	$120.71	$120.70	$120.70
7 purchase totals =	$990.51		$1,050.2244	$1,050.24	$1,050.20	$1,050.20