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	$36.30	3.741%	$37.658	$37.66	$37.65	$37.70
Purchase #2	$82.28	9.503%	$90.0991	$90.10	$90.10	$90.10
Purchase #3	$236.51	13.638%	$268.7652	$268.77	$268.75	$268.80
Purchase #4	$114.92	4.375%	$119.9478	$119.95	$119.95	$119.90
Purchase #5	$76.89	11.726%	$85.9061	$85.91	$85.90	$85.90
Purchase #6	$17.90	4.243%	$18.6595	$18.66	$18.65	$18.70
Purchase #7	$99.61	9.441%	$109.0142	$109.01	$109.00	$109.00
7 purchase totals =	$664.41		$730.0499	$730.06	$730.00	$730.10