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	$136.36	3.557%	$141.2103	$141.21	$141.20	$141.20
Purchase #2	$89.42	12.345%	$100.4589	$100.46	$100.45	$100.50
Purchase #3	$129.30	3.585%	$133.9354	$133.94	$133.95	$133.90
Purchase #4	$84.79	8.264%	$91.797	$91.80	$91.80	$91.80
Purchase #5	$146.59	12.617%	$165.0853	$165.09	$165.10	$165.10
Purchase #6	$196.85	7.422%	$211.4602	$211.46	$211.45	$211.50
Purchase #7	$73.53	7.228%	$78.8447	$78.84	$78.85	$78.80
7 purchase totals =	$856.84		$922.7918	$922.80	$922.80	$922.80