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	$184.91	3.385%	$191.1692	$191.17	$191.15	$191.20
Purchase #2	$210.52	10.859%	$233.3804	$233.38	$233.40	$233.40
Purchase #3	$221.35	7.220%	$237.3315	$237.33	$237.35	$237.30
Purchase #4	$6.79	6.838%	$7.2543	$7.25	$7.25	$7.30
Purchase #5	$120.30	13.478%	$136.514	$136.51	$136.50	$136.50
Purchase #6	$106.32	9.254%	$116.1589	$116.16	$116.15	$116.20
Purchase #7	$249.97	3.664%	$259.1289	$259.13	$259.15	$259.10
7 purchase totals =	$1,100.16		$1,180.9372	$1,180.93	$1,180.95	$1,181.00