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	$100.73	9.488%	$110.2873	$110.29	$110.30	$110.30
Purchase #2	$199.53	3.686%	$206.8847	$206.88	$206.90	$206.90
Purchase #3	$99.28	11.626%	$110.8223	$110.82	$110.80	$110.80
Purchase #4	$113.39	9.207%	$123.8298	$123.83	$123.85	$123.80
Purchase #5	$240.78	13.694%	$273.7524	$273.75	$273.75	$273.80
Purchase #6	$66.91	9.565%	$73.3099	$73.31	$73.30	$73.30
Purchase #7	$229.78	11.804%	$256.9032	$256.90	$256.90	$256.90
7 purchase totals =	$1,050.40		$1,155.7896	$1,155.78	$1,155.80	$1,155.80