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	$123.41	10.838%	$136.7852	$136.79	$136.80	$136.80
Purchase #2	$189.84	3.454%	$196.3971	$196.40	$196.40	$196.40
Purchase #3	$176.83	12.512%	$198.955	$198.96	$198.95	$199.00
Purchase #4	$15.70	9.749%	$17.2306	$17.23	$17.25	$17.20
Purchase #5	$180.58	4.179%	$188.1264	$188.13	$188.15	$188.10
Purchase #6	$194.50	8.443%	$210.9216	$210.92	$210.90	$210.90
Purchase #7	$95.57	3.689%	$99.0956	$99.10	$99.10	$99.10
7 purchase totals =	$976.43		$1,047.5115	$1,047.53	$1,047.55	$1,047.50