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	$47.32	8.276%	$51.2362	$51.24	$51.25	$51.20
Purchase #2	$227.43	3.530%	$235.4583	$235.46	$235.45	$235.50
Purchase #3	$86.49	6.243%	$91.8896	$91.89	$91.90	$91.90
Purchase #4	$32.33	9.641%	$35.4469	$35.45	$35.45	$35.40
Purchase #5	$90.43	9.299%	$98.8391	$98.84	$98.85	$98.80
Purchase #6	$189.31	10.781%	$209.7195	$209.72	$209.70	$209.70
Purchase #7	$11.47	3.702%	$11.8946	$11.89	$11.90	$11.90
7 purchase totals =	$684.78		$734.4842	$734.49	$734.50	$734.40