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	$146.49	13.125%	$165.7168	$165.72	$165.70	$165.70
Purchase #2	$31.79	9.870%	$34.9277	$34.93	$34.95	$34.90
Purchase #3	$124.46	13.557%	$141.333	$141.33	$141.35	$141.30
Purchase #4	$205.98	8.165%	$222.7983	$222.80	$222.80	$222.80
Purchase #5	$73.34	12.783%	$82.7151	$82.72	$82.70	$82.70
Purchase #6	$245.61	6.382%	$261.2848	$261.28	$261.30	$261.30
Purchase #7	$210.32	10.693%	$232.8095	$232.81	$232.80	$232.80
7 purchase totals =	$1,037.99		$1,141.5852	$1,141.59	$1,141.60	$1,141.50