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	$166.87	7.794%	$179.8758	$179.88	$179.90	$179.90
Purchase #2	$88.67	12.289%	$99.5667	$99.57	$99.55	$99.60
Purchase #3	$108.44	11.507%	$120.9182	$120.92	$120.90	$120.90
Purchase #4	$94.78	9.508%	$103.7917	$103.79	$103.80	$103.80
Purchase #5	$241.58	7.443%	$259.5608	$259.56	$259.55	$259.60
Purchase #6	$6.78	9.703%	$7.4379	$7.44	$7.45	$7.40
Purchase #7	$151.38	13.256%	$171.4469	$171.45	$171.45	$171.40
7 purchase totals =	$858.50		$942.5980	$942.61	$942.60	$942.60