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	$180.48	3.799%	$187.3364	$187.34	$187.35	$187.30
Purchase #2	$38.87	9.781%	$42.6719	$42.67	$42.65	$42.70
Purchase #3	$145.51	6.507%	$154.9783	$154.98	$155.00	$155.00
Purchase #4	$199.88	7.835%	$215.5406	$215.54	$215.55	$215.50
Purchase #5	$40.82	3.170%	$42.114	$42.11	$42.10	$42.10
Purchase #6	$236.76	7.747%	$255.1018	$255.10	$255.10	$255.10
Purchase #7	$143.57	3.457%	$148.5332	$148.53	$148.55	$148.50
7 purchase totals =	$985.89		$1,046.2762	$1,046.27	$1,046.30	$1,046.20