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	$135.40	4.245%	$141.1477	$141.15	$141.15	$141.10
Purchase #2	$47.36	8.550%	$51.4093	$51.41	$51.40	$51.40
Purchase #3	$85.98	5.774%	$90.9445	$90.94	$90.95	$90.90
Purchase #4	$109.78	8.790%	$119.4297	$119.43	$119.45	$119.40
Purchase #5	$16.65	10.372%	$18.3769	$18.38	$18.40	$18.40
Purchase #6	$12.29	6.826%	$13.1289	$13.13	$13.15	$13.10
Purchase #7	$104.96	12.605%	$118.1902	$118.19	$118.20	$118.20
7 purchase totals =	$512.42		$552.6272	$552.63	$552.70	$552.50