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	$6.70	4.623%	$7.0097	$7.01	$7.00	$7.00
Purchase #2	$95.64	6.406%	$101.7667	$101.77	$101.75	$101.80
Purchase #3	$78.98	13.753%	$89.8421	$89.84	$89.85	$89.80
Purchase #4	$199.71	5.132%	$209.9591	$209.96	$209.95	$210.00
Purchase #5	$77.79	9.337%	$85.0533	$85.05	$85.05	$85.10
Purchase #6	$84.69	9.223%	$92.501	$92.50	$92.50	$92.50
Purchase #7	$116.95	8.430%	$126.8089	$126.81	$126.80	$126.80
7 purchase totals =	$660.46		$712.9408	$712.94	$712.90	$713.00