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	$126.54	3.829%	$131.3852	$131.39	$131.40	$131.40
Purchase #2	$98.79	12.662%	$111.2988	$111.30	$111.30	$111.30
Purchase #3	$163.51	13.368%	$185.368	$185.37	$185.35	$185.40
Purchase #4	$218.67	3.329%	$225.9495	$225.95	$225.95	$225.90
Purchase #5	$29.95	12.583%	$33.7186	$33.72	$33.70	$33.70
Purchase #6	$186.36	12.257%	$209.2021	$209.20	$209.20	$209.20
Purchase #7	$58.69	8.204%	$63.5049	$63.50	$63.50	$63.50
7 purchase totals =	$882.51		$960.4271	$960.43	$960.40	$960.40