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	$73.61	4.469%	$76.8996	$76.90	$76.90	$76.90
Purchase #2	$83.28	13.373%	$94.417	$94.42	$94.40	$94.40
Purchase #3	$66.61	10.743%	$73.7659	$73.77	$73.75	$73.80
Purchase #4	$245.33	8.396%	$265.9279	$265.93	$265.95	$265.90
Purchase #5	$180.77	8.597%	$196.3108	$196.31	$196.30	$196.30
Purchase #6	$90.92	13.866%	$103.527	$103.53	$103.55	$103.50
Purchase #7	$182.52	3.595%	$189.0816	$189.08	$189.10	$189.10
7 purchase totals =	$923.04		$999.9298	$999.94	$999.95	$999.90