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	$95.72	3.837%	$99.3928	$99.39	$99.40	$99.40
Purchase #2	$58.31	7.850%	$62.8873	$62.89	$62.90	$62.90
Purchase #3	$138.80	5.415%	$146.316	$146.32	$146.30	$146.30
Purchase #4	$199.87	11.218%	$222.2914	$222.29	$222.30	$222.30
Purchase #5	$129.58	12.582%	$145.8838	$145.88	$145.90	$145.90
Purchase #6	$89.86	4.829%	$94.1993	$94.20	$94.20	$94.20
Purchase #7	$112.96	5.796%	$119.5072	$119.51	$119.50	$119.50
7 purchase totals =	$825.10		$890.4778	$890.48	$890.50	$890.50