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	$30.75	3.291%	$31.762	$31.76	$31.75	$31.80
Purchase #2	$98.93	6.368%	$105.2299	$105.23	$105.25	$105.20
Purchase #3	$92.76	3.450%	$95.9602	$95.96	$95.95	$96.00
Purchase #4	$90.31	11.326%	$100.5385	$100.54	$100.55	$100.50
Purchase #5	$167.98	10.281%	$185.25	$185.25	$185.25	$185.30
Purchase #6	$165.68	11.797%	$185.2253	$185.23	$185.25	$185.20
Purchase #7	$168.86	9.124%	$184.2668	$184.27	$184.25	$184.30
7 purchase totals =	$815.27		$888.2327	$888.24	$888.25	$888.30