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	$109.48	5.147%	$115.1149	$115.11	$115.10	$115.10
Purchase #2	$215.72	3.795%	$223.9066	$223.91	$223.90	$223.90
Purchase #3	$140.36	7.178%	$150.435	$150.44	$150.45	$150.40
Purchase #4	$187.31	9.767%	$205.6046	$205.60	$205.60	$205.60
Purchase #5	$28.44	10.811%	$31.5146	$31.51	$31.50	$31.50
Purchase #6	$83.38	5.651%	$88.0918	$88.09	$88.10	$88.10
Purchase #7	$70.59	13.148%	$79.8712	$79.87	$79.85	$79.90
7 purchase totals =	$835.28		$894.5387	$894.53	$894.50	$894.50