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	$89.62	11.502%	$99.9281	$99.93	$99.95	$99.90
Purchase #2	$188.64	7.584%	$202.9465	$202.95	$202.95	$202.90
Purchase #3	$228.53	3.223%	$235.8955	$235.90	$235.90	$235.90
Purchase #4	$37.80	12.134%	$42.3867	$42.39	$42.40	$42.40
Purchase #5	$131.71	7.521%	$141.6159	$141.62	$141.60	$141.60
Purchase #6	$188.44	4.760%	$197.4097	$197.41	$197.40	$197.40
Purchase #7	$116.28	12.155%	$130.4138	$130.41	$130.40	$130.40
7 purchase totals =	$981.02		$1,050.5962	$1,050.61	$1,050.60	$1,050.50