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	$227.50	10.290%	$250.9098	$250.91	$250.90	$250.90
Purchase #2	$17.78	3.775%	$18.4512	$18.45	$18.45	$18.50
Purchase #3	$73.33	9.744%	$80.4753	$80.48	$80.50	$80.50
Purchase #4	$104.41	7.673%	$112.4214	$112.42	$112.40	$112.40
Purchase #5	$174.84	6.155%	$185.6014	$185.60	$185.60	$185.60
Purchase #6	$152.37	11.116%	$169.3074	$169.31	$169.30	$169.30
Purchase #7	$169.82	6.423%	$180.7275	$180.73	$180.75	$180.70
7 purchase totals =	$920.05		$997.8940	$997.90	$997.90	$997.90